DIGESTION IN THE INTESTINE 297 



intestinal mucosa are again decomposed into fatty acids and alkalies, and the 

 alkalies would then be at the disposal of the intestinal contents once more. 



Likewise when the pancreas is extirpated, the utilization of fats is usually 

 much diminished if not entirely stopped; fatty acids are then found in abun- 

 dance in the faeces. The pancreas may be caused to waste away slowly, if its 

 duct be ligated and 0.2 per cent sulphuric acid be injected into the g'land. In 

 this case the absorption of fat declines, but not to any considerable extent until 

 a longer time has elapsed than in the case of extirpation. The cleavage of fat 

 under such circumstances might be brought about either by the enzyme (formed 

 in cells which are still functional) being absorbed and reaching the intestine by 

 some roundabout way, or, as after extirpation, through the agency of Bacteria 

 (Eosenberg). But the question is not yet finally settled. 



If the conception here presented is in the main correct, then the principle 

 upon which the transformation of foodstuffs in the alimentary canal proceeds 

 would be the same for all, namely: they are changed by liydrolytic cleavages 

 into substances which can be brought into solution by the fluids present in 

 the alimentary canal, or by fluids poured into it from the glands. 



The carbohydrates are changed into soluble carbohydrates principally in 

 the intestine. The pancreatic juice plays the chief part in this, although it is 

 assisted by the bile and the intestinal juice. Besides, the Bacteria present 

 act upon the carbohydrates to a considerable extent. In this way, particu- 

 larly in the small intestine, alcohol, lactic acid, acetic acid and succinic acid 

 among other things (Nencki and his pupils) are formed. The acid reaction 

 of the intestinal contents depends in part on these products. 



The intestinal Bacteria have a very special part to play in the herbivorous 

 animals ; for by their agency cellulose is decomposed and the foodstuffs locked 

 up by it are made accessible to the digestive fluids (Tappeiner). 



The participation of Bacteria does not appear to be necessary in the digestion 

 of animal foods, for various polar animals have no Bacteria at all in the intes- 

 tinal contents (E. Lewin). Thierf elder and Nuttal have demonstrated the same 

 thing for guinea pigs fed on milk and finely prepared vegetable food, such as 

 cakes. Schottelius succeeded also in maintaining chicks for a time on perfectly 

 sterile food. But from twelve days on the animals decreased in weight and died 

 of hunger at about the seventeenth day. From this it seems that a coarse vege- 

 table diet cannot be properly and continuously disposed of by the higher animals 

 without Bacteria. And yet it must be added that the facts are by no means 

 sufficient to warrant definite conclusions, for Lewin finds the intestine perfectly 

 sterile in herbivorous polar animals. 



In the lower animals enzymes (cytases) have been demonstrated which them- 

 selves destroy cellulose. The secretion of the snail's liver is an instance (Bieder- 

 mann and Moritz; cf. page 110). 



The putrefactive processes in the intestine are generally restricted within 

 very moderate limits. The reason lies partly in the action of the hydrochloric 

 acid of the gastric juice which reduces the number of Bacteria entering the 

 intestine, and partly in the fact that the foodstuffs as soon as they are suffi- 

 ciently digested, are removed by absorption from the sphere of influence of 

 the Bacteria. 



