^ May, 1908.] Elements of Animal Physiology. 265 



'epitomised as follows. There undoubtedly occurs in the liver a break-up 

 of part of the amino-acids into urea and carbon compounds, the former 

 • being excreted by the kidney, the latter being used as fuel-food or stored 

 as such. In the liver also a polysaccharide called glycogen can ahvays be 

 found. This glycogen increases in amount after the administration of 

 a food rich in carbohydrate and diminishes when the animal is actively 

 exercised. Now glycogen is readil\ transformed into glucose and glucose 

 is found in the blood, but never above a certain small percentage, and 

 it has therefore been suggested that the liver, by means of its glycogen 

 store, keeps the sugar content of the blood up to its normal figure. Part 

 of the digested protein is reformed into true protein taking its place as 

 such, in the blood but where this occurs whether in the bowel wall, in the 

 blood, or in the liver, is difficult to say. Sugars can be changed, as 

 above stated, into glvcogen but this change accounts only for a fraction 

 <,f the total amount absorbed, the rest may probably be altered into fat 

 but in what organ we do' not know. An extraordinary fact bearing on 

 this problem of absorption is that, when the pancreas is removed from an 

 animal, or even if it be merely freed from its attachment to the duodenum, 

 -sugar appears in quantitv in the urine, the animal becomes emaciated 

 .and finally dies. This condition is known pathologically as diabetes but 

 of its origin and significance we know nothing. Water is absorbed to a 

 slight extent in the small intestines making the contents less fluid than 

 ;the chyme. The bile salts are absorbed, returned to the liver, and neutralised 

 by that organ. The cholestrin apparently escapes absorption. 



The activitv of the small intestine is governed largely by the food. 

 Each compound sugar for instance, can excite the secretion of the appro- 

 priate ferment ; and the texture of the food can influence the rate and 

 intensity of peristalsis. But the central nervous system has a considerable 

 -control over the small intestine. Thus during active exercise, when a 

 large number of muscles are employed, the blood vessels of the intestine 

 -constrict and digestion is checked ; moreover the emotional state of the 

 <inimal has, as is well known, considerable influence, whether favourable 

 or unfavourable on digestion. 



DIGESTION IN THE C/ECUM. — The caecum is small in carnivores 

 and man, of moderate size in ruminants and the pig, and very large in the 

 horse. The entrance from the small intestine is controlled by a sphincter 

 called the ileocecal sphincter which in some animals is guarded by a valve- 

 like fold of mucous membrane. In carnivores and man the caecum functions 

 as part of the colon ; but in solipeds, ruminants and the pig, it is a digestive 

 organ of considerable moment. Perhaps the longest sojourn that the food 

 mass makes in its passage through the alimentary canal is made in the 

 •caecum of these animals. In the solipeds its huge size marks it out as 

 having special functions to perform ; m fact when we compare the process 

 of digestion in the horse with that in a ruminant we shall find that in 

 the former animal the proventriculus is comparatively small whilst in the 

 caecum occurs most of the change which takes place in the rumen of the 

 ruminants, with this exception, that in the caecum autolysis is not present 

 l)ut is supplanted bv the action of ferments brought by the food 

 from the small intestine or excreted bv the caecal mucous membrane. Bac- 

 teria also flourish in the caeca of all mammals and it is a matter of debate 

 whether their presence is not absolutely essential. Bacteria certainly help 

 in continuing the digestion of proteins, carbohydrates and fats, but they 

 oan also act in a manner not beneficial. Thus a part of the carbohydrate 

 becomes changed into gases, hydrogen, marsh gas, &c., and so loses its- 

 nutritive properties; and further, from the protein of the food, evil- 



