534 LECTURE XXII. 



pointed out, that the cells come into consideration according to the way 

 that they are constructed, and that evidently chemical processes play an 

 important part in the phenomena. In no case should it be implied that 

 forces unknown to us come into play. It is self-evident that we should 

 recognize clearly just how far we can go in accordance with observed facts 

 and as to where the realms of pure speculation begin. Unquestionably 

 we are at present far from understanding the action of the cells. As long 

 as we do not understand the composition of albumin and especially that 

 of the ferments, we cannot expect to receive much light upon the numerous 

 problems which we meet with in studying the work of the cells. 



The absorption of the individual foodstuffs, their further destiny in 

 the tissues and eventual combustion, we have already considered in detail, 

 so that we will now merely consider one other function of the intestine, 

 namely, the formation of the faeces and their removal from the system. 

 We have already found that the amount of excreta varies with the nour- 

 ishment. The color of the faces changes similarly. Where an abundance 

 of meat is eaten the scybala are dark or grayish colored, while a diet 

 largely of bread makes the color lighter. The bile-pigments have a good 

 deal to do with the color of the faeces, although it is usually their trans- 

 formation product, stercobilin, which is present. The faeces contain besides 

 indigestible substances, the secretion of the intestines and of the accessory 

 glands, and a certain amount of digestible matter which was not absorbed 

 for some reason or other. We also meet with products of putrefaction 

 such as skatole, indole, purine bases, lime and magnesia soaps and other 

 substances. The faeces furthermore always contain inorganic salts, whether 

 it be due to the fact that they were not absorbed from the food, or whether 

 they were eliminated in the intestines. 



The formation of the faeces takes place in the large intestine. Here the 

 unabsorbed material passes, and becomes thickened by loss of water. 

 Without doubt, in the case of the herbivora, the ferments continue their 

 action in the large intestine, and utilize for the organism certain amounts 

 of otherwise undigested material. In the carnivora, however, there is 

 no digestion worth considering in the large intestine. 



We have now mentioned all the functions of the digestive organs. We are 

 well aware that we have failed to give a clear picture of the total work of 

 digestion. Still, we are able to take up certain phases sorhewhat in detail. 

 On the other hand, so many new vistas in this field have been opened 

 up by the investigations of Pawlow and his school and of Bayliss and 

 Starling, and so many new questions remain to be answered, that we no 

 longer can have any doubt that the isolated discoveries obtained here 

 and there will before long be welded together into an organic whole, so 

 that little by little we shall win more and more from the vast field of 

 the unknown. 



