THE AMERICAN NATURALIST [Vol. XLV 



there could be sufficient number of configurational dif- 

 ferences in the corresponding protein molecules of dif- 

 ferent species to account for the specificity of the respect- 

 ive proteins. When, however, we consider that to the 

 serum-albumin molecule alone — and it is by no means 

 the most complex protein — estimates assign the capabil- 

 ity of having as many as ten thousand million stereoi- 

 somers, there would seem to be in this factor of configu- 

 ration alone ample possibilities for the necessities of 

 the case. 



Because of imperfect methods it has in the past been 

 well nigh impossible to "tell how nearly chemically iden- 

 tical corresponding proteins of different species are. 

 Keichert and Brown 13 point out that what formerly 

 passed current as difference in composition may have 

 been due in reality to contaminations or mixtures. "For 

 instance," they go on to say, "the fact that the egg- 

 white of the egg of certain species remains perfectly 

 clear upon boiling, while that of other species becomes 

 opaque, might be taken as meaning a difference in chem- 

 ical composition, but the difference has been shown to 

 lie in the different amounts of alkali and saline present." 

 Again, "The centesimal analysis of corresponding al- 

 bumins and globulins have failed to show any positive 

 differences. Oppenheimer states, from the results of a 

 recent study of serum-albumins of man, the horse and 

 the ox, that serum-albumin is a uniform and specific 

 substance, and that the elementary analyses point to 

 one serum-albumin." This would leave the matter of 

 specificity to be explained solely on the basis of molecu- 

 lar configuration. 



This brings up the whole question of protein consti- 

 tution and configuration. While this is still pretty much 

 a terra incognita still many interesting facts have come 

 to light, and all of them point to the conclusion that we 

 are in no wise compelled to regard the proteins as out- 



13 "The Differentiation and Specificity of Corresponding Proteins and 

 other Vital Substances in Relation to Biological Classification and Organic 

 Evolution: The Crystallography of Hemoglobins, ' ' Publication No. 116, 

 Carnegie Institution of Washington, pp. 1-838, 100 plates, 1909. 



