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Clinical Pathology of Blood

CLINICAL PATHOLOGY OF BLOOD The blood may be considered as a tissue, composed of cellular and intercellular con stituents, the former being the red and white corpuscles and the platelets, and the latter the plasma.

Owing to its coming into intimate association with all other tissues, its examination may afford useful information as to the state of the animal as a whole; also affording particular informa tion in the case of diseases when the causal organism or the more definite lesions are present in the blood.

Methods of Examination The ordinary blood-examination consists of counting the red and white corpuscles, esti mating the amount of haemoglobin, and examin ing stained blood-smears. In special cases the plasma is tested for specific antibodies, e.g. agglutinins.

Procuring the Blood.

Small quantities may be drawn from any superficial vein where the circulation is normal, the ear veins being most convenient; in birds, the comb or under the wing.

The chosen site has the hair clipped, and is washed and dried. The vein is cleanly incised, and when the blood flows the first few drops are wiped away.

Before making the incision any required apparatus should be ready to hand—slides, pipettes, and diluting fluid, etc. so that the required manipulations may be carried out before the blood has time to clot.

If the plasma is to be examined for agglut inins it will be necessary to collect a few c.cm. of blood in a sterile bottle. This is most easily done, in the larger animals at any rate, by drawing blood through a hypodermic needle from the jugular vein.

Counting the Red

Corpuscles The red corpuscles are so numerous that they must be diluted before counting, and for this process a fluid must be used which will not allow the blood to clot and will not injure the corpuscles. Hayem's Fluid combines these qualities and consists of: Mercuric chloride 0 5 gm. Sodium chloride 1 gm. Sodium sulphate 5 gm. Distilled water 200 c.cm.

The most generally used instrument for com bining the processes of dilution and counting of the red corpuscles is the Thoma-Zeiss Hcemo cytometer.

This consists of (1) counting chamber; (2) specially ground cover-glass; (3) red corpuscle pipette; (4) white corpuscle pipette.

The counting chamber is made of an outer flat ring of glass separated by a circular trench from a central platform, both being cemented to a glass slide. The outer ring is mm. higher than the platform, so that the cover-glass resting on it is separated from the platform by mm. The centre of the platform is ruled into minute squares with sides za mm. Thus the area seen on looking down over each small square is x 20x e.mm – 4 0 C As a rule the small squares are enclosed in sets of sixteen by double rulings, and each set of sixteen" small squares" is called a" large square." The red corpuscle pipette is a capillary tube, graduated in tenths up to a mark 1, leading to a bulb which contains one hundred times the volume of the tube, and having above it the mark 101. The bulb contains a glass bead to facilitate mixing the blood with the Hayem's Fluid.

The white corpuscle pipette is similar but the bulb only contains ten times the volume of the tube, the marks being 1 and 11. Its use will be considered in dealing with the leucocyte count.

Procedure. Draw up the fresh blood in the pipette to the mark 1, quickly wipe the tip, and draw up Hayem's Fluid to the mark 101. The bulb now contains blood diluted 1 in 100. The upper mark is 101, and not 100, because the stem of the pipette now contains one volume of Hayem's Fluid which is later discarded. The pipette is rolled round gently, allowing the glass bead to mix the blood uniformly. Next, after blowing away the pure Hayem's Fluid in the stem, a small drop of diluted blood is blown on to the ruled platform and the cover glass lowered gently to avoid bubbles. The drop should be of such size that it does not run over the edge of the platform, and is most easily gauged by squeezing the rubber mouth piece instead of blowing. The droplet is now examined on a level stage with the i-inch objective of a microscope, counting the number of corpuscles in each of the sixteen squares of a large square and drawing an average from the counts of at least five or six sets. As some corpuscles overlap the lines, it is advisable to include in any square those which overlap, say, the top and right - hand side only, those which overlap the other two sides being counted with other squares.

Computation. Each square represents 4 0 c.mm. and the blood is diluted Thus the number of red corpuscles per cubic millimetre is: 4000 x 100 x average number of corpuscles per square. The number computed is of course not absolutely accurate, but the margin of error is comparatively negligible.

A quicker way is to dilute the blood 1-200, in which case the total number of corpuscles counted in five" big squares" followed by 0000 is the number per cubic millimetre of blood.

Counting the Leucocytes The second pipette is used, diluting and a different diluting fluid is used—Thoma's Fluid: Acetic acid (B.P.) 1 c.c.

Sat. sol. Gentian Violet.5 c.c. Distilled water 100 c.c.

With this fluid the red corpuscles are laked and the leucocytes are slightly stained to make them prominent. In this instance only" large squares" are counted, as there are compara tively few leucocytes as compared to reds.

Computation. Each large square is s x x c.mm. c.mm. and the blood is diluted Thus the number of leucocytes per cubic milli metre of blood is 250 x 10 x average number per large square.

Cleaning the Apparatus. The pipettes are washed out with water, then alcohol, and finally ether, but the counting slide must only be washed with water; alcohol or ether would dissolve the cement, and the ring and platform would come unstuck.

Estimation of Haemoglobin The best apparatus is the Gower - Haldane lImmoglobinometer, being a combination of that of Gower and that of Haldane.

In Gower's apparatus a standard tube con tains a solution of carmine identical in colour with 1 per cent blood in water. The blood to be examined is taken in a marked pipette and then expelled into a tube standing beside the standard one and graduated in hundredths. Water is added gradually and the blood mixed continually until the solution is the same as the standard. The graduation on the tube is now read off, and gives the percentage of hwmo globin.

Haldane's method is very similar, but the measured quantity of blood is first laked with about ten volumes of water, and coal gas allowed to flow into the tube. This converts the hwmo globin to carboxyhmmoglobin, and it is com pared when diluted to a standard 1 per cent solution of actual carboxyhmoglobin. This method has the advantage over that of Gower in that the two solutions to be compared are of the same substance; but one must have a supply of coal gas laid on, and this is not always available in country districts.

Tallqvist's HcemoglobinScalemay be employed. This consists of a booklet of absorbent papers. A drop of blood is touched with one of the strips and allowed to diffuse. It is then compared, before quite dry, with a standard scale of tints supplied in the booklet. With this quite simple method the error should not be more than 5 per cent.

Estimation of hemoglobin is as necessary as counting the red corpuscles. For instance in chlorosis the number of corpuscles may be very nearly normal, but they contain little hemoglobin. Conversely in pernicious anemia the corpuscles are greatly reduced, but have a high hemoglobin content. After severe hemo rrhage the reds are reduced, but have a normal hemoglobin content.

Histological Examination Blood may be examined fresh—a drop of blood between slide and coverglass—or fixed and stained in the form of a smear.

To make smears one may put a drop of blood on a slide and spread by touching the drop with the ungummed edge of a cigarette paper and then drawing the paper along. A better way is to put the drop nearer one end of the slide, and then, laying the edge of another slide through the middle of the drop, allow the drop to spread out to the sides of the slide and push or draw the second one along.

Fixing and Staining.In many stains a fixa tive is included, making a preliminary fixation unnecessary.

Separate fixation may be accomplished by immersing the slides in bottles of various fixing reagents, e.g.

1. Absolute alcohol 2. Equal parts alcohol and hour.

3. Formalin, 1 per cent. 1 minute.

Many stains are used for blood, and they vary in usefulness for different purposes. All however act on the same principle. When old, or alkaline, or specially treated solutions of methylene blue are left in contact with eosin, a chemical combination takes place, analogous to an acid combining with a base, and the result ing compound is eosinate of methylene blue.

Jenner's, Wright's, and Leishman's stains combine the processes of fixing and staining. For Giemsa's stain a previously fixed smear is required.

Jenner's Stain. Immerse the unfixed smear in the stain for three minutes, wash in distilled water until it becomes bright pink, dry rapidly by blowing on the smear, and examine direct with (oil immersion) objective.

Wright's and Leishman's Stains. Pour on a counted number of drops of the stain and leave for one minute. Add an equal number of drops of distilled water and leave for five minutes. Wash the smear until it turns pink, dry rapidly, and examine.

Giemsa's Stain. The stain is used, freshly diluted, in the proportion of 1 drop of stain to 1 c.c. of distilled water. The smear must be previously fixed, and the stain is allowed to act for about fifteen minutes.

With all the above stains the basophile elements of the blood take the basic portion of the stain — the blue — and the acidophile elements take the acid portion and stain red.

Basophile elements are: Nuclei of leucocytes, and of red corpuscles if present, and basophile granules of leucocytes (mast cells).

Acidophile elements are: Red corpuscles, granules of polynuclear and eosinophile leuco cytes.

The cytoplasm of the leucocytes stains very faintly blue or not at all, and the granules of eosinophile leucocytes stain more richly red than either the granules of the polynuclears or than the red corpuscles.

In examining stained blood films it is essential to use a (oil immersion) objec tive.

Morphology of the Blood Corpuscles Fled Corpuscles (Erythrocytes). Normally these have the shape of a disc, concave on both surfaces. In the camel, however, they are oval. Mammalian red corpuscles are normally non nucleated, but in birds a nucleus is present and the corpuscles are oval in shape. Their size, and number per cubic millimetre, vary in different animals. In stained preparations, red corpuscles stain pink, and rather more deeply at the periphery owing to greater thickness.

Abnormal Forms. Any variation from the above description denotes an abnormality, except in some cases where the corpuscles appear crenated. This is due to faulty preparation of the film.

When normal in shape, but abnormally small, the corpuscle is known as a microcyte, and if too large as a macrocyte or megalocyte. When varieties in shape occur, such as oval, pear-shaped, fiddle shaped, they are called poikilocytes and the dition spoken of as poikilocytosis. Nucleated red corpuscles are called erythroblasts, and if smaller or larger than a normal corpuscle are called microblasts and megaloblasts respectively. In some conditions also staining is not regularly pink, and a blue coloration is noticed. This may be in the form of a diffuse invasion—poly chromasia or polychromatophilia— or of small well-defined blue points—punctate basophilia or punctate degeneration.

The importance of these abnormalities of red corpuscles is that they indicate disease—usually anemia—although erythroblasts are not rare in very young animals, being probably a per sistence from the foetal state, in which the normal red corpuscles are nucleated. The observation and estimation as to increase or decrease of these abnormalities are of great aid in the prognosis of an from whatever cause.

Leucocytes.There are several kinds of normal leucocytes, which are present in more or less constant proportions, varying of course in different animal species. The only way to find the proportion accurately is to count some hundreds of leucocytes and note how many of each kind are seen. In some diseases, variation from the normal is so pronounced as to make this tiresome procedure unnecessary. Apart from variation in the normal leucocytes, there are conditions in which new ones appear. These will be described after the normal ones.

Normal Leucocytes.There are five varieties: 1. Small Mononuclears (Lymphocytes). In size these are very little larger than the reds, but slightly variable. The nucleus occupies most of the cell and stains deep blue. The cytoplasm.shows as a narrow area of very lightly stained blue around the nucleus.

2. Large Mononuclears (Hyaline leucocytes). These are roughly twice the size of the small mononuclears and stain similarly. The nucleus does not form so large a proportion of the cell and is not usually spherical, being crescentic or kidney-shaped.

Intermediate stages are sometimes noticed between the large and small mononuclears.

3. Polymorphonuclears (Polynuclears). Not quite so large as the large mononuclears. The nucleus is not spherical but variously lobed or twisted. The name of the cell was derived from this characteristic of the nucleus, which may be Z or U shaped. This nucleus stains of a bright lilac tint. The cytoplasm is abundant and contains many fine acidophile granules. These stain very faintly pink in a cytoplasm which stains either very faintly blue or not at all.

In the fowl, however, the picture is very different. The nucleus does not stain so deeply, and the granules are cigar- or spindle-shaped and stain a very deep red. Both in mammals and birds the polynuclear leucocytes are capable of amceboid movements.

4. Eosinophiles. About the same size or slightly larger than the polynuclears, with a similar nucleus. In the cytoplasm are many very coarse, deeply red-staining granules, easily distinguishable from those of the polynuclear by their much greater size and deeper staining. Even in the fowl the eosinophile is easily dis tinguishable as the granules are round, whereas those of the polynuclears are spindle-shaped.

5. Mast Cells (Basophile leucocytes). This is the rarest variety in all animals. They are little larger than the small mononuclears, which they closely resemble. The nucleus, however, does not stain so deeply, and the cytoplasm contains several basophile (blue-staining) or neutrophile (purple-staining) granules.

Abnormal Leucocytes.In severe anmmias one may see immature forms of normal leucocytes, but there are also to be seen two definite forms of foreign leucocyte.

1. Basophile Myelocyte. Large cells—even larger sometimes than the large mononuclears —with a roughly spherical nucleus. Both nuclei and protoplasm stain palely and the latter is granular, making the myelocyte distinguishable from the large mononuclear in which the proto plasm is hyaline.

2. Eosinophile Myelocyte. Similar to the last, but the granules in the protoplasm stain red. They are easily distinguished from the normal eosinophile in having a round nucleus.

Blood Plates. These are organized elements found in normal blood, being flat and about one third the diameter of red corpuscles. They are very difficult to detect, and unless special methods be employed are not seen in smears. In the fowl, however, there are nucleated oval cells homologous with the mammalian blood plates. These are not quite so long, and about half the breadth of the red corpuscles. With blood stains, the nucleus is seen to be blue and the cytoplasm a paler blue. They are known as thrombocytes.

On the following page is a table of the approximate average constitution of the blood as regards the red and white corpuscles in various animals. As the variations of the normal are so wide it necessarily follows that the figures given are only approximately accurate.

Variation in Numbers of Blood Elements 1. Variations in the number of Bed Corpuscles. Increase in the number is known as Poly cythcemia, and decrease as Oligocythcemia or Ancemia. There are many physiological causes of variation in blood count. For instance, younger animals have a higher count than adults; males have a higher count than females or neuters; animals living at high altitudes have a higher count than normal average.

Administration of purgatives concentrates the blood by simple extraction of water.

Pathologically polycythcemia may be due to profuse diarrhoea, vomition or exudation; in the last, due perhaps to pneumonia or ascites. Lack of sufficient drinking water will produce the same effect.

anemia is due pathologically to many factors —limmorrhage, malnutrition, loss of activity of blood-forming organs, and destruction of red corpuscles being the commonest. Haemorrhage and malnutrition need no further discussion. Loss of activity of blood-forming organs may be due to specific diseases, especially when accompanied by toxin formation. Poisoning by lead, mercury or arsenic will produce the same effect by lessening blood formation.

Destruction of the red corpuscles is a feature of many pathological processes, mainly septic invasions, septicmmias, pneumonia, tuberculosis, equine hfflmoglobinuria (azoturia), and many protozoan diseases (various redwaters).

Decrease in number of the red corpuscles to any degree is always accompanied by alteration in the appearance of the persisting corpuscles. According to the severity one observes variation in size, poikilocytosis, polychromasia, punctate degeneration, nucleated red corpuscles, and eventually introduction of myelocytes into the circulation.

2. Variation in the Number of Leucocytes. If the number is increased this condition is leucocytosis, and if diminished, leucopenia. Phy siological variations are common and follow various stages of digestion, parturition, and violent exercise. Very young animals con stantly show a leucocytosis. Leucocytosis does not necessarily involve an increase in the number of all the varieties of leucocytes, and similarly with leudopenia.

(a) LEIICOCYTOSIS. Digestion in ruminants and herbivora generally causes a very small rise in numbers; if noticeable the polynuclears increase. Carnivora, however, show a large increase in small mononuclears (lymphocytosis) some hours after a big meal. One should bear this in mind when attempting a normal count, or the result may be misleading. New-born animals have a high number of leucocytes, espe cially of lymphocytes, returning gradually to the normal in a few weeks as a rule. Violent exercise induces a polynuclear leucocytosis.

Pathologically any acute inflammation causes leucocytosis, especially suppurative processes.

In this case the polynuclears are mainly increased, and the more vigorous the resistance of the animal to the infection, the greater the leuco cytosis. The common veterinary leucocytosis accompanies strangles, pleurisy, pneumonia (of all kinds), quittors, abscesses, etc., and tetanus. Experimentally, leucocytosis is induced by introduction into the system of various chemical or bacterial products, the former class producing usually a transient effect. Camphor, quinine, pilocarpin, nuclein, strychnine, ethereal oils, and many metallic salts will cause leucocytosis.

Haemorrhage also is followed at an interval of several hours to a few days by increase in the number of leucocytes, being roughly in pro portion to the amount of blood lost and to the recuperative power of the patient. It is thus a good guide to prognosis in cases of severe hmmorrhage.

The main individual leucocytoses and their causes are as follows: Lymphocytosis. Normally this occurs more in the young than in adults. Pathologically, lymphocytosis is most commonly seen in try panosomiasis.

Eosinophilia (increase in eosinophiles). The greatest and most common cause is helmin thiasis. Almost any worm infestation may be responsible—ascarides, tapeworms or scleros tomes; markedly so in the case of the last named. Skin diseases may also be a cause, in direct proportion to the actual irritation caused, rather than to the extent of skin invaded. Thus in mange one would expect a greater degree of eosinophilia than in eczema.

Eosinophiles are diminished in malignant organic diseases, being almost absent immedi ately before death.

Polynuclear Leucocytosis.Noticed in cases of pneumonia and all septic infections, e.g. fistulous withers, quittor, strangles, empyema. As the condition is constant in septic infections, it may aid in the diagnosis of deep-seated pus.

Hyaline Leucocytosis.This is not commonly noticed in this country. Some degree of it accompanies protozoan diseases, e.g. redwater.

.Mast Cell Leucocytosis is very rare and may be seen in leukaemia.

Myelocytes.These foreign cells are seen in leukaemia and advanced anemia. They are also occasionally seen accompanying polynuclear leucocytosis.

(b) LEIICOPENIA (decrease in leucocytes). As in leucocytosis, not all varieties are equally affected. It is usually only noticeable following destruction of tissues responsible for leucocyte formation—as in tuberculosis or some other toxic diseases. Malnutrition and general debility other than debility due to worms may cause it. The condition may be induced experimentally with tannin, atropin.

Special Diseases affecting the Blood Pernicious Aneemia. This disease produces the most striking changes in the blood elements of any blood disease. It is entirely different from the homonymous human disease, having more the characters of a severe secondary anemia. The red corpuscles are reduced, show ing microcytes and megalocytes. Poikilocytosis, punctate degeneration and polychromasia, with presence of nucleated red corpuscles, are all to be seen. Leucocytes are also reduced, but not so much as the reds; giving a spurious impression of leucocytosis.

The cause of the disease is usually obscure in animals and few cases are ordinarily seen.

Leukaemia (Leucocythmmia). A primary disease of the blood-forming organs, and very rarely seen in the lower animals, possibly owing to the infrequency of blood examination. Two forms are recognized, viz. Mixed - celled or Myeloid Leukaemia and Lymphatic Leukaemia. In both forms there is great increase in the number of leucocytes and decrease in red cor puscles. In the former a great proportion of the new leucocytes are myelocytes, whereas in the latter they are mainly lymphocytes—even over 90 per cent of the total.

In both forms the spleen, lymphatic glands, and bone marrow show hyperplasia, but these structures are not softened, being either as firm as, or firmer than normal owing to simultaneous corresponding increase in connective tissue.

Throughout the body, in capillaries and lymph spaces, excess of leucocytes is observed, the variety seen being dependent on the form of leukaemia present.

Lymphatic leukaemia is the only form so far observed in the lower animals.

Pseudoleukmmia (Hodgkin's Disease). Also sometimes called Lymphoma The main anatomical features are exactly similar to those in true leukaemia, viz. enlarged lym phatic glands, spleen and bone marrow, but it is easily distinguished in that the proportion of leucocytes in the blood is approximately normal. Of the domesticated animals the dog is the only one in which this condition is not rare.

General and Infectious Diseases affecting the Blood Changes observed in the blood accompanying various diseases vary with the class of disease. For example, in septic inflammations, pneumonia, and tetanus there is leucocytosis, mainly poly nuclear; in anthrax or fowl cholera the specific organisms themselves are to be found in the circulating blood; in glanders and contagious abortion, specific agglutinins are present in solution in the plasma, and proof of their presence is utilized in diagnosis. Again, hel minthiasis will produce eosinophilia, and mono nuclear leucocytosis is common in protozoan invasions.

Strangles. In

the early febrile stages the blood is concentrated owing to dehydration. Later polynuclear leucocytes are increased. When the abscess ruptures or is incised the leucocytes return to normal.

Equine Pneumonia.

Very similar blood features to strangles. There is primary concen tration of the blood owing to the fever, giving the impression of polycythwmia. Later leuco cytosis is seen, mainly polynuclear, and the number of red corpuscles becomes subnormal. The occurrence of leucocytosis is a favourable sign, but if the initial polycythffimia persists to the exclusion of leucocytosis, prognosis is very unfavourable, indicating in all probability necrosis or gangrene.

Fowl Cholera. In

naturally occurring cases, the blood symptoms are those of anemia with moderate leucocytosis. Blood from a bird dead of the disease will show the causal organisms bipolar-staining bacilli.

Anthrax.In cattle and sheep the blood is extensively invaded by the bacilli a short time before death; so constantly, in fact, that if they are not to be found at the time of death in a suspicious case, one may be certain that anthrax is not the cause of death. In horses the organisms are present in the vast majority of cases, but in pigs death often occurs before the blood stream is invaded. The changes in the blood itself are very small. There may be a slight leucocytosis and anmia following dis integration of red corpuscles. The most im portant features are the dark colour and tarry consistency, and the fact that it does not clot.

Microscopical examination is limited to a search for anthrax bacilli. Any of the Roman owsky stains are suitable, but the best method is M' Fadyean's. This method has the advan tage of using a thick smear and is performed as follows: A thick smear is air-dried by waving the slide rapidly, and then incompletely fixed by heat, the slide being heated in a flame until only just uncomfortably hot to the back of the hand. The smear is now stained with 1 per cent methylene blue for a few seconds, washed thoroughly, and dried by blotting. When examined under the objective the bacilli are stained blue with a pinkish capsule, or if the capsules are broken up the material appears as pinkish amorphous masses. This pink reac tion of the capsular material is even visible to the naked eye, for when the stained smear is held obliquely to the light it is seen to be a distinctly reddish blue, quite different from normal blood.

Glanders. In the early stages of acute glanders there is a concentration of the blood, but later a moderate anmia, accompanied by polynuclear leucocytosis. This latter becomes more pronounced when the disease assumes clinical proportions. In non-clinical cases the leucocytosis is said to be rendered more pro nounced within twenty-four hours by the ad ministration of mallein. Glanders is one of the diseases in which an appreciable amount of specific agglutinin is found in the plasma, and this is constantly used in some countries in diagnosing the disease—agglutination test.

Tuberculosis.The blood changes in obscure cases are almost negligible; in fact within the bounds of normal variation. In advanced chronic cases there is said to be anmia, but this is often unrecognizable as the blood is concentrated. Some investigators claim to get positive agglutination results with the serum, whereas others have completely failed.

Specific (or Contagious) Abortion.Mares, cows, and ewes are affected, the common form being induced in each case by a specific organism {mare, Bacillus abortivo-equinus; cow, Bacillus abortus, Bang; sheep, a vibrio or spirillum). The only important change is the formation of a specific agglutinin in the plasma, but there is no visible change in the blood. One may diagnose the specific infection by drawing off some blood in a small sterile bottle, centri fuging after clotting, and testing the agglutin ating power of the serum on emulsions of the specific organisms.

Protozoan Diseases Texas Fever.A piroplasmosis due to Piro plasma (or Babesia) bigeminum in cattle. In the acute stages the causal parasites are seen in the blood in the form of pale pear-shaped bodies, usually in pairs inside the red corpuscles. With the usual blood stains the cytoplasm of the parasites is pale blue, with a red chromatin body, near the pointed end. Irregular forms are seen, but in typical cases the two pointed ends of two parasites are close together with the bodies lying at a very acute angle to one another, being often almost parallel.

Usually only a small proportion of the cor puscles is invaded—often less than 2 per cent, but in fatal cases up to 10 per cent may be affected before death.

The changes in the blood elements are the result of invasion by the piroplasms. A large number of red corpuscles is destroyed, the count being reduced often to 2, 000, 000. Accom panying this destruction the signs of anmia appear—nucleated reds, poikilocytes, poly chromasia, etc. Leucocytes are increased, par ticularly the lymphocytes, and after recovery the number is said to remain higher than normal.

British Redwater.Similar as regards blood changes to Texas fever, but the causal piro plasm is Babesia divergens (M`Fadyean and Stockman), so-called because two parasites in a red corpuscle lie at a very obtuse (divergent) angle to one another, often being almost end to end.

Canine Piroplasmosis (Malignant Jaundice of Dogs). Caused by Babesia canis and is a very widespread disease.

The parasite is very like B. bigeminum, and further resembles it in that only a very small proportion of corpuscles is invaded. A striking point, however, is that, as the disease progresses, although the percentage of invaded corpuscles is low, any single corpuscle may contain a large number of parasites-12 or 16. In chronic cases so few corpuscles are invaded that there is great difficulty in finding them.

The blood changes in acute cases are similar to those in Texas fever—a progressive, severe anemia, accompanied by leucocytosis; but in this case the increase is mainly in the poly nuclears (Nocard).

Biliary Fever in Horses (Equine piroplasmosis). This disease has two causal organisms Babesia caballi and Nuttallia equi. Clinically the two are said to differ slightly. In the acute febrile stages the parasites are found in the red corpuscles. B. caballi has a morphology and distribution singly or in pairs similar to B. bigeminum. N. equi is a more slender parasite, and its most typical form is just after division, which is into tetrads, so that the corpuscle shows four parasites all at right angles to one another like a" Maltese cross" (Nuttall).

A larger number of corpuscles is usually affected than in Texas fever or malignant jaundice—up to 10 per cent or more in severe cases. Adminis tration of quinine lowers the Maltese cross forms of N. equi by inhibiting division (Theiler).

The blood changes are exactly parallel to those in Texas fever.

Sheep Piroplasmosis ( Carceag), due to Babesia ovis and common in Eastern Europe. The morphology of the parasite and the blood changes are very similar to those in Texas fever.

Babesia mutans.Described by Theiler, occur ring in South Africa, often in company with other parasites. The parasite itself is fairly harmless, but is important in that it may be mistaken for a stage of Theileria parva, the causal parasite of East Coast fever.

B. mutans is smaller and more rod-shaped than B. bigeminum.

East Coast Fever (Rhodesian Tick Fever). The causal parasite is Theileria parva. Most of the life-cycle of this parasite is passed out side the blood stream--mainly in the lymphatic system. However, towards the end of the course of the attack, sexual forms of the parasite appear in the red corpuscles. They are rather small and rod-shaped. A larger number of red corpuscles is invaded as time progresses. During the course of the disease the parasite is not present in the blood, but there is a great increase in mononuclear leucocytes.

Trypanosomiasis.Any disease caused by a trypanosome is so named. All trypanosomes membrane. From the centrosome rises a fla gellum which runs along the free edge of the undulating membrane and is usually continued beyond its limit. The anterior end is the one towards which the flagellum runs, since the organism moves with this end foremost. Multi plication is asexual by vertical fission. Most trypanosomes are 20-30µ long.

As it is very difficult to distinguish the various trypanosomiases clinically, so is it to recognize the individuals in the blood. However, the combination of clinical symptoms and a blood examination renders diagnosis more feasible. The blood symptoms are similar in all cases. There is a progressive diminution in reds, low haemoglobin content, and mononuclear leueo cytosis. Towards the end (death) of the disease myelocytes appear in the blood.

Examination for presence of trypanosomes may be made with a drop of fresh blood between slide and cover-glass. In these circumstances one may see the moving trypanosomes or notice that the red corpuscles are being agitated by some body. To attempt to identify a trypano some individually a stained smear is necessary.

Trypanosomes are spread from animal to animal by parasites—probably always by biting flies, in whose digestive tract the trypanosome sometimes undergoes a certain development. There is one most important exception, viz. Dourine or Mal de Colt, which is spread only by copulation.

The table below shows the most common trypanosomiases.

Diseases of Indefinite Origin.These diseases are mainly due to ultra - visible viruses, e.g. rabies, rinderpest, swine fever, and equine pernicious or infectious anemia.

The virus although invisible and filtrable are a common general structure, varying with the individual species. There is a fusiform body with a large nucleus and a second chromatin body called the centrosome or blepharoplast. Along one side of the body is a filmy undulating may be present in the blood; which can be proved in positive cases by animal inoculation with filtered blood.

With rabies the leucocytes, mainly the poly nuclears, increase constantly up to the point of death. In rinderpest there is an initial increase, then a decrease, and finally another increase. In swine fever and equine perni cious or infectious anemia, on the other hand, there is a steady decrease both in leucocytes and red corpuscles, and in the latter disease the ordinary blood signs of anemia.

Helminthiasis. The blood may afford useful accessory evidence in aid of diagnosis. In all forms of helminthiasis, but chiefly in scleros tomiasis, there is a pronounced eosinophilia so that cases of colic of obscure origin may be dia gnosed as resulting from worm infection. Acute indigestion or impaction does not materially affect the leucocytes, and in enteritis there is polynuclear leucocytosis.

In some cases of fflariasis, as in the case of Filaria immitis in dogs, the worm embryos themselves may also be present in the blood.

Acariasis (Mange). If severe, acariasis will induce eosinophilia, particularly in dogs and cats. It appears that the degree of eosino philia is in direct relation not to the extent of infestation but to the amount of actual irritation or severity of dermatitis. Sarcoptic mange is the best example, and this of course has a simpler method of diagnosis.

corpuscles, red, leucocytes, normal and leucocytosis