50 THE ALBUMINS. 



small amounts. Neutral solutions of the mucins are precipitated by 

 alcohol in the presence of neutral salts. Similar results are obtained 

 with some of the salts of the heavy metals. 



On heating with dilute hydrochloric acid (2 per cent.) on a 

 water-bath the carbohydrate group is split off and can be demon- 

 strated with Fehling's test (see Urine). 



Certain mucoids, after partial hydrolysis with alkalies, give a 

 fine cherry-red color on treating with dimethyl-amido-benzaldehyde 

 and heating (Ehrlich). 



Whether or not some of the hyalogens belong to the order of the 

 gluco-albumins remains to be seen. Like these, they contain a 

 nitrogenous carbohydrate radicle which is probably chitosamin. 

 Such bodies have been described especially by Krukenberg. 

 They comprise the neossin of edible Chinese swallow-nests ; the 

 membranin found in Descemet's membrane, and the capsule of the 

 crystalline lens ; the spirographin of the spirographic membrane ; 

 the holothurian mucin ; the chondrosin of certain mushrooms, and 

 others. The hyalin which is found in echinococcus cysts, and the 

 onuphin of the tubes of Onuphis tubicola, are probably not albu- 

 minous. The same is true of chitin, which with other hyalins has 

 been found in the extraskeletal and intraskeletal parts of various 

 animals. 



The Keratins. Formerly the keratins were classed with the 

 albuminoids, and were not regarded as true albumins. It has been 

 conclusively established, however, that, like these, they contain 

 the guanidin remnant, leucin, radicles of the glutaminic acid group, 

 ornithin (as arginin), the cystin group, as well as an ^-thiolactic 

 acid nucleus ; further, phenyl-alanin, a tyrosin and indol radicle, 

 as also a carbohydrate group. Especially characteristic is the large 

 amount of sulphur (35 per cent.) which is obtained in toto as 

 cystin on hydrolytic decomposition. Tyrosin, in some members of 

 the group, notably in human hair, is obtained only in small amount. 

 Analysis of some keratins has given the following results : 



Hair, 



C = 50.65 H == 6.36 N = 17.14 S = 5.00 O = 20.85 



C = 49.85 H = 6.52 N = 16.80 S = 4.00 O = 23.20 

 Egg-shell membranes . C == 49.78 H = 6.64 N = 16.43 S = 4.20 O = 22.90 

 Neurokeratin . . . . C = 56.11 H = 7.33 N = 11.46 S = 1.87 



The keratins are the most important constituents of the epi- 

 dermal structures of the body. They are found in the horny layer 

 of the epidermis, in hair, in hoofs, horns, nails, and feathers; further 

 in the egg membranes of birds, of various reptiles and fishes, etc. 

 A neurokeratin is found in the axillary sheath of the medullated 

 nerves. 



The keratins are all insoluble in water, dilute acids, and alka- 

 lies. Strong acids and alkalies cause their solution, but at the 

 same time bring about their disintegration. A solution of keratin 

 can therefore not exist. 



