DIGESTION IN THE LARGE INTESTINE. 429 



Ligation of caeca in chickens caused diarrhoea, loss of flesh, and 

 death from inanition. 



The most important function of the caecum is, in all probability, to 

 be found in the digestion of cellulose, which occurs in it. It is well 

 known that from 30 to 40 per cent, of cellulose disappears in passing 

 through the intestinal canal of the horse, and the poorer the food is in 

 true nutritive substances the greater will be the amount of cellulose 

 digested. Experiment has proven that the saliva, gastric juice, and 

 pancreatic secretion are entirely inactive on cellulose. On the other 

 hand, the fluids collected from the small intestine of a newly killed 

 horse have been found to dissolve from 40 to 78 per cent, of cellulose 

 (Hofmeister), and this power is lost when these fluids are previously 

 boiled r indicating the probable dependence of this digestive process on a 

 true ferment. Admitting these facts, the share which the caecum bears 

 in digesting cellulose is evident; it acts as a reservoir for fluids and 

 undigested food-stuffs coming down from above, and by its reaction, 

 temperature, etc., favors fermentative changes. 



The nature of the substances resulting from the digestion of cellu- 

 lose are clouded in obscurity : the most natural presumption would be 

 that it was converted into sugar, but no experimental proof of this has 

 ever been adduced, though it is generally assumed that the cellulose in 

 digestion is changed into some nutritive substance, which is absorbed. 

 According to this, cellulose should be classed among the food-stuffs. 

 "Unfortunately, this also does not admit of proof. It is well known that 

 in fermenting cellulose may be converted into marsh-gas, and Hofmeis- 

 ter's experiments seem to prove that the substance resulting from the 

 digestion of cellulose by the intestinal fluids of the horse is gaseous in 

 nature. While this may be so, and there is no denying that the gas may 

 be met with in the alimentary canal, it does not follow that all the 

 digested cellulose is converted into marsh-gas. For, as Ellenberger has 

 pointed out, we often meet with a lactic acid fermentation of sugar in 

 the stomach and intestine, but do not infer from that that all the sugar 

 which disappears from the alimentary canal has been converted into 

 lactic acid. The case may be similar with cellulose ; when in excess, or 

 not needed, it may and probably is converted into marsh-gas ; when 

 needed by the economy, it is absorbed in some soluble form, probably of 

 the nature of a sugar. This view is supported by the fact already 

 alluded to, that the poorer the food the greater the quantity of cellulose 

 which disappears. 



2. The Functions of the Colon. — The colon in the carnivora con- 

 stitutes a simple reservoir for excrementitious matters, and in the her- 

 bivora it is doubtful if it has a more important r61e to perform in the 

 digestive elaboration of food. In the walls of the large intestine are 



