432 PHYSIOLOGY OF THE DOMESTIC ANIMALS. 



to the substernal curvature, then they mount to the pelvic curvature 

 ■which is always higher than the sternal curvature, and then up the dia- 

 phragmatic curvature, and finally descend abruptly, passing by the left 

 kidney to enter the convolutions of the floating colon, where they make 

 two ascents and two descents (Fig. 165). 



The large intestine of the ox is shown in Fig. 166. 



The interior arrangement of the colon consists in the formation of 

 pockets, in which portions of the contents remain temporarily, while the 

 centre of the gut is free. The disposition of certain parts of the colon 

 leads to a difference in the physical characters of its contents at different 

 points. The diaphragmatic curvature, on account of its dependent posi- 

 tion, contains large volumes of liquid, in which certain salts are abundant, 

 such as ammonio-phosphate of magnesium, especialty after oat diet, and 

 in this locality these salts are often deposited as intestinal calculi. 



Digestion in the large intestine cannot, therefore, be said to take 

 place, although absorption is highly active, and numerous cases are on 

 record in which life has been preserved through the absorption by the 

 walls of the large intestine alone of alimentary substances introduced 

 into the rectum. In the large intestine complex fermentations take 

 place, and true decomposition frequently occurs in the contents of this 

 portion of the alimentary tube, especially when the reaction is alkaline. 

 Many of the gases, such as oxygen and nitrogen, which are found here 

 have probably entered witli the food ; others are derived from different 

 fermentations ; thus, for example, hydrogen is liberated in the butjric 

 acid fermentation, sulphuretted hydrogen and ammonia from the putre- 

 faction of animal substances. 



XI. THE COMPARATIVE DIGESTIBILITY OP DIFFERENT FOOD-STUFFS. 



The quantity and chemical composition of the faeces is of special 

 interest on account of the insight which it permits as to the degree of 

 digestibility and convertibility of the different food-stuffs, for it is evi- 

 dent that if we know the amount and composition of any food given to 

 an animal for a series of days, the loss of these materials, determined by 

 an analysis of the faeces, will indicate within certain limits the amount 

 which has been digested and absorbed in its passage through the body. 

 In making these calculations, however, it must be remembered that a 

 large amount of fluid is added to the food in the form of the digestive 

 juices, which, to be sure, is again largely absorbed ; but we have further 

 seen that certain excretory ingredients have been added to the faeces, 

 and, further, that the different food-stuffs may undergo decompositions 

 other than digestive in the alimentary tract. The digestive processes, 

 as we have seen, are of the same nature in all our domestic animals, 

 simply varying in degree. This difference we have also seen to be clue to 



