358 PHYSIOLOGY CHAP. 



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ash constituents and other non-nitrogenous substances (ethereal 

 extracts). 



The final conclusions arrived at by Prausnitz may be summed 

 up as follows : 



(a) There is no fundamental difference between plant and 

 animal foods as regards their utility in the human intestine. 

 Assimilation and absorption depend rather on their preparation 

 (cooking, trituration) than on their animal or vegetable origin. 



(&) The foods best utilised or absorbed are those of vegetable 

 origin (rice, white bread or other preparations of finely ground 

 flour), only small traces of which are found in the faeces. With 

 the most profitable animal food, on the contrary, e.g. meat, un- 

 digested residues are always found in the faeces, although in 

 small quantities only. Milk and cheese give more copious faeces, 

 which are relatively poorer in nitrogen as compared with meat, 

 because they yield a larger amount of mineral residues. 



(c) Human faeces, with few exceptions, consist chiefly not of 

 alimentary residues, but of the excretory products of the intestine. 



(d) The quantity of faeces depends principally on the nature 

 of the food, some kinds requiring more succus entericus for their 

 digestion than others. It seems, therefore, more accurate to 

 differentiate the foods into those which cause the production of 

 much or little faeces than to speak of foods which can be more or 

 less assimilated. 



V. Stich (1853) was the first who directed attention to the 

 fact that faecal matters contain substances which have a toxic 

 action on the living body. He saw that if excreta were intro- 

 duced per os or per rectum from one animal into another of a 

 different species, more or less serious symptoms of intoxication set 

 in. From the fact that the toxic substances which habitually 

 accumulate in the alimentary canal are normally innocuous to 

 the animals which manufacture them, he was led to think that 

 each kind of animal has the power of destroying the toxins which 

 it produces. He assigned a predominating importance to the 

 protective action of the epithelium in resistance to auto- 

 intoxications of intestinal origin (cf. also Chapter V. 14). 

 But the other facts we have discussed show that this protective 

 function is at any rate shared by the liver, which arrests or 

 converts not a few of the poisons absorbed by the roots of the 

 portal system. 



Without entirely rejecting the protective function of the in- 

 testinal epithelium in Stich's sense, its excretory function, i.e. the fact 

 that by its means many katabolic products are eliminated from the 

 blood and mix with the faeces and gases of the intestine, is certainly 

 admitted by almost every doctor. This theory is based on a 

 number of suggestive observations, both clinical and experimental, 

 some of which attracted the attention of Bouchard. It is a fact 



