February 14, 1908] 



SCIENCE 



245 



not radically different from those obtained 

 hy Osborne and others. Far more prob- 

 able is it that there are still undiscovered 

 a number of component parts of the pro- 

 tein molecule, knowledge of which must 

 be obtained before we can hope to arrive 

 at a synthesis of protein. Physiologists 

 have long sought this goal. It means so 

 much in the unraveling of many intricate 

 problems in protein metabolism, in nutri- 

 tion in general, in intracellular reactions 

 and particularly those which bear upon 

 the changes incidental to fertilization and 

 cell division. 



To how great degree the large variety 

 of proteins of both animal and vegetable 

 tissues have chemical and physiological in- 

 dividuality has long been an unsettled 

 question. There is plenty of physiological 

 evidence that the circulating proteins con- 

 tained in the blood and lymph of different 

 species of animals are unlike each other in 

 some respects at least. Blood serum from 

 one species introduced into the circulation 

 of another species causes marked disturb- 

 ance and even a fatal result. Animal pro- 

 teins are plainly different in some respects 

 from those of vegetable origin, while the 

 latter derived from different sources vary 

 greatly among themselves. We can readily 

 conceive of individual proteins playing 

 quite different parts in the nutrition of 

 man and of animals when taken as food. 

 There may be radical and logical differ- 

 ences in the nutritive value of animal as 

 compared with vegetable proteins, although 

 at present we have no positive proof of 

 such differences. Arguments for or 

 against vegetarianism, which are now 

 based primarily upon questions of senti- 

 ment, may in time rest upon a solid 

 foundation of fact. Such observations as 

 have been made bearing upon the consti- 

 tution of proteins are beginning to have 

 special significance because of the radical 

 differences in chemical make-up shown by 



the individual proteins studied. Take, for 

 example, phaseolin from the kidney bean. 

 This protein, as shown by both Osborne 

 and Abderhalden, yields about 15 per 

 cent, of glutaminic acid, 4 per cent, of 

 lysine, 2.5 per cent, of proline, 5 per cent, 

 of arginine, etc. Excelsin from the Brazil- 

 nut, on the other hand, yields by hydrol- 

 ysis 16 per cent, of arginine, 13 per cent, 

 of glutaminic acid, 1.6 per cent, of lysine 

 and 3.6 per cent, of proline; while the 

 hordein of barley yields no lysine whatever, 

 but furnishes 36 per cent, of glutaminic 

 acid and nearly 14 per cent, of proline. 



Such differences as these must have some 

 significance; they certainly indicate a 

 totally different assortment of building 

 stones in the finished structure, and it is 

 fair to presume that they carry with them 

 some influence upon the physiological be- 

 havior of the proteins when the latter are 

 taken as foods. The gliadin of wheat 

 yields by hydrolysis about 37 per cent, of 

 glutaminic acid, while the casein of cow's 

 milk yields only 11 per cent. Here is in- 

 dicated a radical difference in structure 

 between the protein of animal origin and 

 that derived from the plant kingdom. We 

 can not say, however, that vegetable pro- 

 teins are characterized by a high content 

 of glutaminic acid, for while it may be 

 true of both gliadin and hordein, it is not 

 the case with phaseolin or excelsin, both of 

 which yield only a little more glutaminic 

 acid than animal casein. Plainly, we have 

 here a problem not to be overlooked, and 

 in these days of specialized vegetable foods 

 we may justly expect an adequate explana- 

 tion of the physiological significance to be 

 attached to these chemical differences in 

 structure. The gliadin of wheat, the zein 

 of corn meal and the hordein of bai-ley 

 are all three alcohol-soluble proteins. This 

 solubility in warm alcohol might well serve 

 to place these proteins in a group by them- 

 selves, but they plainly are unlike chemi- 



