202 A MANUAL OF VETERINARY PHYSIOLOGY 



jected under the skin, digests the tissues and produces ulcera- 

 tion. Faeces and urine are very irritating, excepting, so to speak, 

 in their own home. The bladder never shows any sign of irrita- 

 tion from the presence of urine, but if it be paralysed, and the 

 urine, in dribbling away, falls on the skin, the part in time 

 ulcerates, and very early becomes excoriated. Even tears 

 running over the face, in cases of obstruction of the duct, cause 

 the skin to ulcerate. In spite of the action of gastric juice, 

 ' bots ' live in the stomach for months, and, unfortunately, are 

 never digested. Parasites of the digestive tract enjoy the same 

 immunity from digestion that the membrane of the canal 

 possesses. 



It is now generally believed that the immunity enjoyed by 

 the tissues in contact with active or irritating secretions is due 

 to the local formation of an antibody. That in the stomach 

 has been named antipepsin, and its function is to neutralise 

 the digestive action of the gastric juice on the living wall. 



We have never yet met with post-mortem digestion of the 

 stomach in the horse ; whether this be due to the horse's acid 

 being mainly or wholly lactic cannot be definitely stated. 



The Gases of the Stomach. — The nature of these largely 

 depends upon the food — for example, green food is most pro- 

 ductive of gas, owing to the active fermentation it undergoes. 

 Traces of oxygen, a quantity of carbonic acid, and variable 

 amounts of marsh-gas, sulphuretted hydrogen, hydrogen, and 

 nitrogen, are found. The oxygen and nitrogen are derived from 

 the swallowed air, the carbonic acid is derived from the fer- 

 mentation of the food and the action of acids on the saliva, 

 while the marsh - gas is obtained by the decomposition of 

 cellulose. 



The gases from the intestines of the horse and rumen of the 

 ox are very commonly inflammable, and burn with a pale blue 

 flame. This is due to marsh-gas, which may be readily ignited 

 when mixed with a due proportion of oxygen. 



Vomiting and Rumination. 



Vomiting amongst solipeds and ruminants is rare, but the 

 act is common in the dog and pig. 



The reasons given as to why the horse does not ordinarily 

 vomit are various : (i) The thickened and contracted cardiac 

 extremity of the oesophagus ; (2) the oblique manner in which 

 the latter enters the gastric walls ; (3) the dilated pylorus lying 

 close to the contracted cardia, so that compression of the 

 stomach contents forces them into the duodenum ; (4) the 

 cuticular coat thrown into folds over the opening of the cardia ; 



