2IO PHYSIOLOGICAL CHEMISTRY. 



tive tract there may be a great increase of unutilized nitrogen. 

 This is more especially true of failures in the pancreatic diges- 

 tion than it is of failure in the work of the stomach. 



Proteins. The most important question to consider here is 

 that of proteins themselves in the feces. Nitrogen in other 

 forms has a far different meaning since it may represent bodies 

 which have been already digested and absorbed, and then 

 thrown into the intestine again. But nitrogen as protein rep- 

 resents practically waste in most cases. Among the protein 

 substances which may be found sometimes in feces these may 

 be mentioned : albumins proper, casein, nucleo-proteids, albu- 

 moses, peptones and naturally more or less of certain albu- 

 minoid bodies which are digested with difficulty. The certain 

 detection of all these bodies under all conditions is not always 

 possible with our present knowledge. Some of the simplest 

 of the tests employed will be briefly mentioned. The soluble 

 substances only are considered here. 



Albumins. Acidify the fresh feces with dilute acetic acid and extract 

 with distilled water. The acid prevents casein and mucin from going 

 into solution at the same time. Filter through good Swedish paper and 

 apply tests to the nitrate. Albumose and peptone go into solution with 

 this treatment 



Albumins proper are coagulated by heating the nitrate, while the de- 

 rived proteins do not respond to this test. The albumins give also the 

 biuret test and are precipitated by solution of potassium ferrocyanide in 

 presence of acetic acid. But albumose, not peptone, responds to the same 

 test. 



Albumoses and Peptones. By extracting as above, coagulating any albu- 

 min possibly present and filtering, the filtrate may be used for albumose 

 and peptone tests. In the filtrate free from albumin zinc sulphate or am- 

 monium sulphate may be used to precipitate albumose. In the filtrate 

 from this peptone may be recognized by the biuret test. 



Casein. This is. sometimes found in the feces of children on a milk 

 diet. To recognize it these tests may be made. The fresh feces may be 

 extracted first with rather weak sodium chloride solution to take out solu- 

 ble albumins, then with weak acid to complete the removal of such bodies. 

 The casein may next be brought into solution with sodium hydroxide, not 

 too strong, and obtained in the filtrate. In such a filtrate acetic acid pro- 

 duces a voluminous precipitate if casein is present, but mucin is also pre- 

 cipitated. Casein, however, redissolves in an excess of acetic acid while 

 mucin does not. After filtering the casein may usually be thrown out 



