112 THE PROTEIN SUBSTANCES. 



to KOSSEL and WEISS l depends at least in part, to a racemisation of the 

 hexone bases, especially arginine within the protamine molecule. They 

 give the biuret test beautifully, but with the exception of cyclopterine, 

 jS-cyprinine and crenilabrine do not give MILLON'S reaction. The pro- 

 tamine salts are precipitated in neutral or even faintly alkaline solutions 

 by phosphotungstic acid, picric acid, chromic acid, and alkali ferrocy- 

 anides. 



The protamines are prepared, according to KOSSEL, by extracting 

 the heads of the spermatozoa, which have previously been extracted 

 with alcohol and ether, with dilute sulphuric acid (1-2 per cent), filtering, 

 and precipitating with 4 vols. of alcohol. The sulphate may be purified 

 by repeated solution in water and precipitation with alcohol, and if 

 necessary, conversion into the picrate. For more details see the works 

 of KOSSEL and MALENUCK. The double-platinum salt is best suited 

 for analysis and can be obtained, according to GOTO, by precipitating 

 the methyl-alcohol solution of the protamine hydrochloride with plat- 

 inum chloride. MIESCHER also precipitates the base as a double-plat- 

 inum salt. 



B. Albuminoids or Albumoids. 



Under this name we collect into a special group all those protein 

 bodies which cannot be placed in either of the other groups. Most and 

 best studied of the bodies belonging to this group are important con- 

 stituents of the animal skeleton or the cutaneous structure. Some are 

 hardened secretions, and all occur as a rule in an insoluble state in the 

 organism, and they are distinguished in most cases by a pronounced 

 resistance to reagents which dissolve proteins, or to chemical reagents 

 in general, and it is due to these external properties that they are put 

 in a special group. From a purely chemical standpoint there is no 

 reason why they should be separated from the true proteids in a special 

 group. Most of the bodies belonging to the albuminoids have been 

 given on page 92. 



The Keratins. Keratin is the chief constituent of the horny struc- 

 ture of the epidermis, of hair, wool, of the nails, hoofs, horns, feathers, 

 of tortoise shell, etc., etc. Keratin is also found as neurokeratin (KUHNE) 

 in the brain and nerves. The shell membrane of the hen's egg seems 

 also to consist of keratin, and according to NEUMEISTER 2 the organic 

 matrix of the eggshells of various vertebrate animals belongs in most 

 cases to the keratin group. 



1 Zeitschr. f. physiol. Chem., 59, 60, and 78. 



2 Ktihne and Ewald, Verb. d. naturhistor.-med. Vereins zu Heidelberg (N. F.) ; 1; 

 also Kiihne and Chittenden, Zeitschr. f. Biologic, 26; Neumeister, ibid., 31. 



