556 WASTE-PRODUCTS 



the slightest degree. Then, again, even upon a standard diet, the out- 

 put of indican may be expected to vary greatly with the type of infect- 

 ing organisms in the intestine. Thus Herter has shown that Bacillus 

 coli communis produces indole but only traces of skatole, which is 

 the methyl derivative of indole, while certain anaerobic putrefactive 

 bacteria produce skatole, in preference to indole, from tryptophane. 

 Skatol does not appear to be normally excreted in the urine, at least 

 in the form of a conjugated sulphuric acid. 



Phenol-sulphuric Acid and Cresol-sulphuric Acid are constant con- 

 stituents of urine, and, as in the case of indican, the output is obviously 

 derived from the products of intestinal putrefaction. It is probable 

 that these substances, of which the total excretion may amount to 

 fifty milligrams per day, originate from the putrefactive decomposi- 

 tion of Tyrosine and Phenylalanine. 



In general it may be said that while aliphatic alcohols, terpenes and 

 many phenols are excreted in the urine in conjugation with glucuronic 

 acid, the greater part of the phenols and polyphenols are excreted in 

 conjugation with sulphuric acid. Yet a third vehicle of excretion is 

 that afforded by conjugation with Glycocoll, or ammo-acetic acid. 

 Thus Benzole Acid, appears in the urine after administration in the 

 form 9f the conjugated Hippuric Acid : 



C 6 H 6 COOH + CftNHzCOOH = C6H 5 COHNCH 2 COOH + H 2 O 

 Benzole acid. Glycocoll. Hippuric acid. 



Hippuric acid is a very abundant constituent of the urine in 

 Herbivora, comparatively scanty in the urine of Carnivora, and inter- 

 mediate in amount in the urine of partially herbivorous animals like 

 ourselves. The daily excretion in man, subsisting upon a normal 

 mixed diet, is about 0.7 grams, but after eating quantities of vegeta- 

 bles or fruits it may rise as high as 2 grams. 



The synthesis of hippuric acid from benzoic acid and glycocoll is 

 accomplished within the tissues of the kidneys themselves. This, in 

 fact, was the first synthetic process which was definitely shown to take 

 place in animal tissues (by Schmiedeberg and Bunge) and also the 

 first to be performed by admixture of the components of the reaction 

 with macerated tissue. It is not improbable, however, that some 

 measure of hippuric acid synthesis may also occur in other organs. 



When large amounts of benzoic acid are administered to animals the 

 elimination of glycocoll is far in excess of the glycocoll which could be 

 obtained by simple hydrolysis of the protein. " Thus McCollum and 

 Hoagland brought a pig into a condition of minimal nitrogen metab- 

 olism by administering a diet of starch containing 75 calories per 

 kilogram body-weight. To this diet was then added varying amounts 

 of benzoic acid, and finally hydrochloric acid and benzoic acid were 

 given together. The total nitrogenous output and its partition among 

 the various nitrogenous fractions in the urine were determined ifr the 

 different periods of the experiment with the following results: 



