420 



SCIENCE 



[N. S. Vor. XXVIII. No. 718 



comparisons in respect to their physical 

 properties and the proportion of their de- 

 composition products, so that those which 

 are alike in their more apparent characters 

 have been still further distinguished from 

 one another. Whether these are in fact 

 chemical individuals, must await the de- 

 velopment of new methods of study. For 

 the present they must be accepted as the 

 simplest units with which we can deal. 



SUITABILITY OF SEED PROTEINS FOB A STUDY 

 OF PROTEIN CHEMISTRY 



The various proteins thus established 

 furnish material for further study, and are 

 characterized by wide differences not only 

 in physical properties, but in the propor- 

 tion of their decomposition products. 

 They can be prepared in large quantity 

 in a high state of purity, and, being a part 

 of the reserve food stored up for the nutri- 

 tion of the developing embryo, are by na- 

 ture more stable than the animal proteins 

 which form a part of physiologically active 

 tissues. Furthermore, they are not asso- 

 ciated with tissues and fluids rich in other 

 forms of protein from which they are to be 

 separated, and they are mostly obtained in 

 the form of dense precipitates, often 

 crystalline, which are little inclined to ad- 

 sorb other substances from which they can 

 afterwards be separated with difficulty. 

 Although associated intimately in the seed 

 with many forms of soluble and insoluble 

 carbohydrates, they can, in many cases, be 

 separated from every trace of the latter, as 

 is shown by appropriate reactions. 



It is my firm belief that a careful ex- 

 amination of them will ultimately afford 

 a better knowledge of the chemistry of pro- 

 teins in general than can be obtained from 

 proteins of animal origin. Although the 

 problems immediately connected with the 

 animal proteins are of greater importance 

 to physiology than those at present recog- 



nized as connected with seed proteins, 

 there is no question but that definite knowl- 

 edge of the chemistry of seed proteins will 

 be directly applicable to many important 

 problems of animal physiology. 



THE DIFFERENT GROUPS OF PROTEINS FOUND 

 IN SEEDS 



The seed proteins for the most part can 

 be grouped in much the same way as the 

 proteins of animal origin, but in so doing, 

 it is necessary to modify to some extent the 

 requirements to which the animal proteins 

 belonging to some of these groups are at 

 present assumed to conform. The neces- 

 sity of some scheme of classification for the 

 proteins is recognized by all who write or 

 teach about them, and although the present 

 method of classifying proteins according to 

 their solubility is wholly unsatisfactory 

 from a purely chemical standpoint, it is 

 practically the only one now available. 

 On chemical grounds there is no more 

 reason for dividing the proteins into two 

 groups of animal and vegetable proteins, 

 than there is for making a similar distinc- 

 tion between the carbohydrates. I have, 

 therefore, endeavored to assign the various 

 forms of seed proteins to the commonly 

 recognized groups established for those of 

 animal origin, and have proposed to 

 slightly modify the definitions usually 

 given for these groups, but only so far as 

 this is necessary. 



1. Globulins form much the greater part 

 of the reserve protein of all seeds except 

 those of the cereals. By globulin is meant 

 protein soluble in solutions of neutral salts 

 but insoluble in water. This defimition 

 does not strictly apply to many of the seed 

 proteins assigned to this group, for these 

 behave as globulins only under certain 

 conditions. As these conditions prevail 

 during the extraction and isolation of 

 these proteins and depend on the presence 

 of free acid in the extracts, it is important 



