EXPERIMENTAL. 17 



EXPERIMENTAL PART. 



Although positive evidence of the chemical individuality of protein sub- 

 stances can not yet be obtained, there is no question that protein preparations 

 can be isolated from seeds and animal tissues which, beyond doubt, represent 

 distinctly different substances. Thus five unquestionably different forms 

 of protein, differing in composition, solubility, and physical characters, can 

 be isolated from the wheat kernel. Whether each of these is itself a chem- 

 ical individual or a mixture of two or more very similar substances can not 

 at present be asserted. All that can be said is that it has not yet been pos- 

 sible to separate them into fractions, the properties of which indicate a 

 mixture. 



Owing to the extreme sensitiveness of proteins to the action of acids, 

 alkalis, and salts, the minor differences in solubility are not to be depended 

 upon as a basis for characterizing individual proteins. Thus the protein 

 edestin, which in pure water is entirely insoluble, in the presence of a slight 

 amount of acid is freely soluble therein. The addition of a small quantity 

 of a neutral salt throws the edestin out of this acid solution, while a larger 

 quantity of salt at once redissolves it. 



Such differences in solubility have nothing to do with the protein mole- 

 cule proper, but depend on the formation of protein salts, the solubility of 

 which is different from that of the free protein itself. As the formation of 

 such protein salts depends on conditions that in most cases can not be taken 

 into account, such differences in solubility can not be made a basis for char- 

 acterizing the different individual proteins. 



We are therefore limited, in dealing with such problems, to the more marked 

 differences in solubility, such as that in alcohol, strong saline solutions, or 

 alkalis, and to constant ultimate composition of successive fractional precip- 

 itations. Thus, when proteins have been separated into fractions which 

 have the same composition, general solubility, and physical properties, we 

 are not justified in concluding that we have in hand a single individual pro- 

 tein. All we can conclude is that we have reached the limit of separation 

 attainable with the means now available, and that for the present we must 

 accept such products as the simplest units with which we can now deal and 

 which for the present must serve as our basis for further study. If, on the 

 other hand, protein preparations, characterized in the manner above de- 

 scribed, show distinct and constant differences from one another, we are 

 justified in considering them to be different substances. 



That the wheat kernel contains at least five such distinct protein sub- 

 stances will be shown in the following pages. 



