148 CHEMICAL STATICS 



That casein will combine with various alkaloids to form water- 

 soluble compounds has been shown by W. A. Osborne (89). 

 From the marked effects of caffeine upon the viscosity and con- 

 ductivity of gelatin in hydrochloric acid solutions Pauli and 

 Falek (93) infer that caffeine enters into combination with gelatin 

 hydrochloride. The compounds which the various dyes form 

 with amino-acids have been studied by Suida (116). 



5. The Compounds of Proteins with Soap and Lipoids. — It 

 has been pointed out by Rona and Michaelis (106) that the 

 power of soaps, such as sodium oleate, to reduce the surface 

 tension of water, is much diminished by the presence of proteins, 

 and they infer that the soaps form compounds with protein. 

 No such effect was observed when esters, such as amyl acetate, 

 tributyrin, propyl acetate or ethyl butyrate were employed 

 instead of soaps. These results have been confirmed by Berczeller 

 (17). It has long been known that it is an extremely difficult 

 matter to free proteins from contamination with lecithin, and 

 the existence of lecithin-protein compounds has frequently been 

 inferred from this fact (48) (87) (95). More decisive evidence 

 of the existence of such compounds has recently been brought 

 forward by Feinschmidt (27) and Allemann (5) who have shown 

 that the optimal H+ concentration for the precipitation of vari- 

 ous proteins is very considerably modified by the presence of 

 lecithin. 



Fatty acid compounds of the peptones have been prepared by 

 Izar and di Zuattro (54) by the action of chlorides of the fatty 

 acids upon peptones at low temperatures. The compounds thus 

 prepared contain from 18 to 20 per cent of fatty acid. 



6. The Compounds of Proteins with Proteins and their Pos- 

 sible Significance in Life Phenomena. — It has been shown by 

 Kossel (62) that the protamins, which, it will be recollected, 

 are strongly basic proteins, when added to weakly alkaline solu- 

 tions of other proteins give rise to precipitates. Kossel believes 

 that the compounds which are thus formed between the pro- 

 tamins and less basic proteins are analogous to the naturally 

 occurring histones (63) (66). Hunter (53) has further investi- 

 gated these compounds and finds that while crystallized egg- 

 albumin, casein, hemi-elastin, gelatin, edestin, heteroalbumose, 

 protalbumose, "alkali-albuminate" and histone sulphate yield a 

 precipitate in alkaline solution upon the addition of clupein. 



