218 PHYSIOLOGICAL CHEMIS1RY. 



the addition of hydrolichloric acid, are precipitated by picric acid. 

 The picrate precipitate is then distilled with ammonia. The two 

 bodies are obtained from the distillate by repeated shaking with 

 ether and evaporation of the several ethereal extracts. The residue, 

 containing indol and skatol, is dissolved in a very small quantity of 

 absolute alcohol and treated with 8-10 vols. of water. Skatol is 

 precipitated, but not the indol. The further treatment necessary 

 for their separation and purification will be found in other works. 



The gases which are produced by the putrefactive processes are 

 mixed in the intestinal tract with the atmospheric air swallowed 

 with the saliva, and as the gas generated by different foods vary, 

 so the mixture of gases after various foods should have a dissimilar 

 composition. This is found to be true. Oxygen is only found in 

 very faint traces in the intestine; this may be accounted for in 

 part by the formation of reducing substances in the fermentation 

 processes which combine with the oxygen, and partly, perhaps 

 chiefly, to a diffusion of the oxygen through the tissues of the walls 

 of the intestine. To show that these processes take place mainly 

 in the stomach the reader is referred to page 189, on the composi- 

 tion of the gases of the stomach. Nitrogen is habitually found in 

 the intestine, and it is probably due chiefly to the swallowed air, 

 or perhaps in part, as BUNGE claims, to a diffusion of nitrogen 

 from the tissues of the intestinal walls to the intestine. The 

 * carbon dioxide originates partly from the putrefaction of the pro- 

 teids, partly from the lactic-acid and butyric-acid fermentation of 

 carbohydrates, and partly from the setting free of carbon dioxide 

 from the alkali carbonates of the pancreatic and intestinal juices 

 by their neutralization by the hydrochloric acid of the gastric juice 

 and by organic acids formed in the fermentation. Hydrogen occurs 

 in largest quantities after a milk diet and in smallest quantities 

 after a purely meat diet. This gas seems to be formed chiefly from 

 the butyric-acid fermentation of carbohydrates, although it may 

 occur in large quantities in the putrefaction of proteids under cer- 

 tain circumstances. There is no doubt that the sulphuretted 

 hydrogen which occurs normally in the intestine originates from 

 the proteids. The marsh-gas undoubtedly originates in the putre- 

 faction of proteids. As proof of this RUGE found 26.45$ marsh- 

 gas in the human intestine after a meat diet. He found a still 



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