SOAPS, PROTEIN DERIVATIVES AND TISSUES 227 



of the peptization and coagulation type, (2) of the heat coagulation 

 type and (3) of the physiological coagulation type. 



2 



Peptization may be discussed by reference to the well-known 

 changes suffered by a protein " insoluble " in water, such as 

 casein, when this is subjected to the action of any of the light 

 metal alkalies. Casein, like any of the pure higher fatty acids 

 (for example palmitic), when mixed with water fails " to dissolve." 

 Expressed in the terms developed in connection with the theory 

 of the lyophilic soap colloids, 1 the casein and the palmitic acid are 

 neither soluble in water nor yet solvents for water. When, how- 

 ever, an alkali (like sodium hydroxid) is added to either, both 

 become " soluble." In the case of the fatty acid we have long 

 said that the change is coincident with transformation from fatty 

 acid to a soap; in the case of casein (and similar proteins) however, 

 we have more commonly said that it is " soluble " "in alkaline 

 solutions," that it is " peptized " by alkalies, that it " becomes 

 colloidally dispersed through a requisite number of 'OH ions," 

 etc. It simplifies matters and is more correct to say that what 

 happens is the same in both sets of materials. From the casein, 

 too, is formed a soap-like compound (namely sodium casemate) 

 which is not only more soluble in water but also a better solvent 

 for water than the original " neutral " casein. As the soaps are 

 best thought of as definite compounds, each with its own solubility in 

 water and its own solvent power for water, so also is it best to conceive 

 of the basic and metallic proteinates also as definite chemical com- 

 pounds possessed of their own solubility in water and solvent power 

 for water. 



The idea that alkalies (or acids) unite with protein to yield new 



compounds is, by itself, of course, not new. It was early expressed 



n : 1 1 i<l I.. I i KBERM ANN 2 and has, since their studies, 



been confirmed and developed by W. B. HARDY, 3 WOLFGANG PAULI,* 



Seepage64. 



8. BUOARSKY and L. LIBBERMANN 1 Miner's An h . 72, 61 (1898). 



It H Md.^ .l,,ur I'hysiol., 33, 2. r l (1906). 



' U DLpriANo PAULI: Kolloidc IH mie der Eiweiaskdrper, 09, Dresden (1920) 

 where may be found the reference* to his earlier studies. 



