198 PHYSIOLOGICAL CHEMISTRY. 



tinal toxins has been isolated and definitely recognized, but 

 with them other bodies are formed which are readily detected 

 in the urine, as is the indican referred to above. In the urine 

 of typhoid fever, and of other pathological conditions also, cer- 

 tain complex aromatic products are always present which give 

 rise to the well-known reaction designated as the diazo reac- 

 tion of Ehrlich. When a mixture of weak solutions of sodium 

 nitrite and sulphanilic acid is added to this pathological urine 

 under certain conditions it strikes a carmine to garnet red 

 color, due to the formation of an azo compound of some kind. 

 The urine must add an aromatic body, different from those 

 normally present, to aid in the formation of this azo coloring 

 substance. With normal urine an orange color is usually 

 obtained, but this deeper red is characteristic of some bacterial 

 product probably, of the exact nature of which we are still 

 in ignorance. 



THE FECES. 



Composition. In the lower intestine the absorption, of 

 water is one of the most important of the changes taking place 

 and this leaves what remains in a semi-solid condition ready 

 for final discharge. The amount of water left in the feces is 

 quite variable, and although the fecal mass may appear hard 

 the water content is usually 70 to 85 per cent. In the thinner 

 pathological discharges it may be much higher. 



At first sight it might appear that the feces should consist 

 mainly of undigested residues, and this was long held to be 

 the case ; but we now know that such substances may make up 

 the least important part of the discharge. The several kinds 

 of products present may be roughly divided as follows : 



1. Bacteria. 



2. Products formed by bacteria. 



3. Remains of the digestive ferments. 



4. Epithelium and mucus from the intestinal walls. 



5. Food residues partly or wholly undigested. 



In the normal fecal discharge all these groups are repre- 

 sented, but incidentally there may be many other things pres- 



