Gas may be liberated from cylinders and pro pelled over the enemy lines by the aid of the wind, but the more common method is to com press the noxious fumes in a casing in the shape of a shell, which is then fired in much the same way as an ordinary shell.
The essential feature of the gas is that its specific gravity must not be lower than that of the atmosphere, otherwise diffusion would be too rapid to produce the desired effect; further, it must be of an irritant or poisonous nature, so as to produce the greatest inconvenience or possibly death to those with which it comes into contact.
Different types of gas have made their appear ance from time to time; thus some appear to exert a particular effect upon the ocular appar atus, producing an intense smarting sensation and a copious flow of tears; these are known as lachrymatory gases. Others, from their irritant effect upon the cutaneous membranes, have been termed"mustard gas." Chlorine was at one time largely employed, but its use has now been partly superseded by the production of various other gases, no doubt considered more objectionable.
Since many of these gases are irritant or caustic, more especially when they come into contact with moist surfaces, it follows that the respiratory apparatus would be amongst the first to suffer; also in animals those parts not well protected by hair, such as the perineum.
In a typical case of gas poisoning, provided the animal has been exposed for some little time, the following train of symptoms will be observed: Loss of appetite, buccal mucous membranes blistered, nostrils and Schneiderian membrane excoriated, and in many cases the lips, and anus also. The skin is hot and painful, and after a few hours shows numerous cracks and fissures from which an exudate com mences to ooze and runs off the hair in drops.
In the course of a few days the condition of the buccal mucous membrane and skin will commence to improve, but respiratory symptoms usually present themselves, as marked by shallow jerky respiration and slight mucoid discharge from the nostrils. The breath then becomes
foetid and characteristic of gangrene of the lungs. Exudate may appear in the chest, with oedema of the breast and fore-limbs. Gangrene of the lungs then becomes more marked, and death may ensue in from seven days onwards.
Cases of gas poisoning may be divided into acute and subacute. Some animals are more susceptible than others, as is evidenced by the fact that amongst animals exposed for an equal period some get off very lightly whilst others develop fatal symptoms.
Instances have been observed in which the symptoms are chiefly confined to the respiratory organs. In the early stages these simulate con gestion of the lungs. Thus, there may be accelerated and laboured breathing and an appearance of acute distress, with the head held low and dilated nostrils, from which a frothy or mucoid discharge appears. The visible mucous membranes assume the appear ance seen in congestion of the lungs. The temperature is elevated somewhat.
Irritation of the respiratory mucous mem branes is evidenced by a painful hacking cough, the discharge assumes a yellow colour and becomes purulent and offensive. Should the patient survive long enough gangrene usually supervenes.
Treatment.Prognosis must depend upon the degree to which the animal has been exposed.
Minor cases tend to recover spontaneously. Absolute rest is essential, diet should be attended to, and the appetite tempted with carrots and similar foodstuffs.
Hygiene plays an important role; warmth and a good supply of fresh air are absolutely essential.
In certain experimental cases, bleeding fol lowed by intravenous injections of physiological saline solution has given encouraging results. The inflamed skin and mucous membranes must be treated on general principles. Carron oil or similar dressings may be used for the skin.
In the event of recovery, a long convalescence is essential.