226 PHYSIOLOGICAL CHEMISTRY 



color of the calomel stool is generally believed to be due to biliverdin. 

 v. Jaksch, however, claims to have proven this view to be incorrect 

 since he was able to detect hydrobilirubin (or urobilin) but no biliverdin 

 in stools after the administration of calomel. The bismuth stool was at 

 one time thought to derive its color from the black sulphide which is 

 formed from the subnitrate of bismuth. We now know 1 that the color 

 is due to the reduction of the bismuth compound (subnitrate) to bismuth 

 suboxide. In cases of biliary obstruction the grayish-white acholic 

 stool is formed. 



Under normal conditions the odor of feces is due to skatole and 

 indole, two bodies formed in the course of putrefactive processes occur- 

 ring within the intestine (see page 215). Such bodies as methane, 

 methyl mercaptan, and hydrogen sulphide may also add to the disagree- 

 able character of the odor. The intensity of the odor depends to a 

 large degree upon the character of the diet, being very marked in stools 

 from a meat diet, much less marked in stools from a vegetable diet, and 

 frequently hardly detectable in stools from a milk diet. Thus the stool 

 of the infant is ordinarily nearly odorless and any decided odor may 

 generally be readily traced to some pathological source. 



A neutral reaction ordinarily predominates in normal stools, although 

 slightly alkaline or even acid stools are met with. The acid reaction is 

 encountered much less frequently than the alkaline, and then commonly 

 only following a vegetable diet. 



Experiments in which the actual hydrogen ion concentration of the 

 feces was determined indicate that the reaction of the excreta is uni- 

 formly slightly alkaline.' 2 ' Pronounced dietary changes, e.g., low protein 

 diet, high protein diet, fasting, water drinking with meals, produce at 

 most only minor changes in the reaction of the feces. 



The form and consistency of the stool is dependent, in large measure, 

 upon the nature of the diet. Under normal conditions the consistency 

 may vary from a thin, pasty discharge to a firmly formed stool. Stools 

 which are exceedingly thin and watery ordinarily have a pathological 

 significance. In general the feces of the carnivorous animals are of a 

 firmer consistency than those of the herbivora. 



The continued ingestion of a diet which is very thoroughly digested 

 and absorbed is frequently accompanied by the formation of dry, hard 

 fecal masses (scybala) . Constipation generally results, due to the small 

 bulk of the feces and its lack of moisture. At present the formation of 

 scybala is considered pathological, as an expression of spastic constipa- 

 tion. To counteract this tendency toward constipation the ingestion 



1 Quincke: Miinch. med. Woch., p. 854, 1896. 



2 Howe and Hawk: Jour. Biol. Chem., u, 129, 1912. 



