570 METABOLISM, NUTRITION AND DIETETICS 



the regulation of the ferment action, which is a characteristic 

 property of the normal cell, becomes feebler the longer it is with- 

 drawn from normal conditions. Similar autdlytic processes have 

 been observed in the spleen, muscle, lymph-glands, kidneys, lungs, 

 stomach wall (independently of pepsin), thymus, and placenta; 

 also in pathological new growths like carcinoma, in the breaking 

 down of which and in the removal of such exudations as occur in 

 the alveoli in pneumonia, these proteolytic ferments seem to play 

 a part. It is to be assumed that the syntheses of the proteins or 

 their products, which are scarcely less characteristic of the tissue 

 cells than the decompositions effected by them, are also due to 

 the action of separate intracellular ferments or upon the reversed 

 activity of the proteolytic ferments. 



More direct proofs of the production of ammo-acids in the tissues 

 are not lacking. A rare condition known as cystinuria has been 

 alluded to on a previous page (p. 482). Here there is a continuous 

 excretion of the sulphur-containing amino-acid cystin in the urine. 

 Sometimes the cystin is accompanied by other amino-acids, as 

 leucin and tyrosin, a condition which might be called amino- 

 aciduria. Cystinuria, while of course resulting from a gross anomaly 

 in metabolism, is of little clinical importance unless the sparingly 

 soluble cystin should form calculi somewhere in the urinary tract. 

 The most plausible explanation of the condition is that in the 

 normal course of the metabolism each of the ' building-stones ' of 

 the proteins is sooner or later further decomposed by special fer- 

 ments, and that for some reason the ferment which acts on cystin 

 is absent, or if it is still produced, the conditions are more or less 

 unfavourable to its action. Unable to take its place in the meta- 

 bolic current, except in so far as it can be utilized to form taurin, 

 and therefore taurocholic acid for this property it has not lost 

 cystin becomes a chemical outcast in the body of the cystinuric 

 individual, and is got rid of by the kidneys as an ' unemployable/ 

 By comparing the amount of cystin excreted with the amount 

 ingested in the food-proteins and with the (undiminished) amount 

 contained in the tissues (especially the hair and the nails, since 

 keratin is exceptionally rich in cystin), it has been shown that a 

 portion of the cystin in the urine must have come from the tissues 

 (Abderhalden). Observations on animals in prolonged starvation 

 afford additional evidence. The hair and nails continue to grow 

 and to maintain the high cystin content, and taurocholic acid con- 

 tinues to be excreted. In like manner glycin continues to be pro- 

 duced and to unite with cholic acid to form the glycocholic acid of 

 the bile. 



There are other and more striking proofs that glycin can be 

 formed in the body in large amount. For example, as already 

 stated (p. 475), when benzoic acid is ingested it is not excreted as 



