THE SKIN AND ITS APPENDAGES. 415 



shavings contain even more, viz., 3.42, of which 2.53 is loosely 

 combined. 



In addition, we find a variable amount of salts, among which the 

 insoluble forms are especially important. Their presence manifestly 

 serves the purpose of increasing the rigidity of these structures. 

 Especially noteworthy is the large amount of silicic acid which is 

 found in hair and in feathers. Besides this, we meet with variable 

 amounts of phosphates and sulphates of the alkalies and alkaline 

 earths, and very curiously also with iron salts. The fact that larger 

 amounts of the latter are found in dark-colored hair than in hair 

 of a lighter color suggests that their presence may be dependent 

 upon these pigments. Of interest is the fact that Gautier was able 

 to demonstrate the presence of traces of arsenic as a constant con- 

 stituent of the skin and its appendages, viz., the hair, the wool of 

 sheep, etc. 



The black and brown pigments which are found in the hair and 

 in the skin of the negro belong to the group of the melanins. 

 Individually these bodies are but little known, and it is an 

 open question whether the iron that is found in the ash is present 

 in these structures in molecular combination with the pigments. 

 Unlike the fuscin of the choroid and the hippomelanin that has been 

 obtained from melanotic tumors in horses, the melanins of the skin 

 and the hair are easily soluble in solutions of the alkaline hydrates. 

 They contain sulphur (2 to 4 per cent.), but not in so large amounts 

 as the phymatorhusin that has been isolated from melanotic growths 

 of man and from the urine (8 to 10 per cent.). Bodies belonging 

 to this order apparently have also been encountered among the 

 products of hydrolytic decomposition in the case of the common 

 albumins, and Pick has described a similar substance which he found 

 in Witte's peptone, and which he designates as peptomelanin. Con- 

 jointly the melanins, which can be obtained from the albumins, are 

 termed melanoidins (Schmiedeberg). On fusion with potash skatol 

 and indol result ; heated in the dry state with powdered zinc they 

 give an intense pyrrol reaction with pine wood and hydrochloric acid. 

 On reduction of the melanoidin obtained from serum-albumin with 

 zinc in a current of hydrogen, as also from the melanin of the 

 choroid, and that of melanotic growths, pyridin has been obtained. 

 In addition Samuely found a supposedly aromatic body with a 

 benzaldehyde-like odor. 



As regards the origin of the melanoidins, we may imagine that 

 the various chromogenic groups which occur in the albumins, and 

 which contain or form aromatic (tyrosin) and mainly heterocyclic 

 radicles (pyrrol, pyridin, skatol), are condensed to dark-colored 

 products on boiling with acids, with coincident loss of water and 

 taking up of oxygen, and that the mixtures of these products 

 represent the melanoids. 



E. Spiegler seems to have demonstrated conclusively that the 



