No. 533] NUCLEUS AND CYTOPLASM IN HEREDITY 295 



justified, therefore, in inferring from these results that 

 the differences between corresponding proteins in dif- 

 ferent species of a genus are rather to be referred to 

 differences in molecular configuration than in atomic 

 composition of the molecule. 



The case of haemoglobin is only one of several lines of 

 evidence that might be brought forward as indicating 

 the specificity of proteins. The serum-albumins which 

 constitute the very font of the living molecules of higher 

 animals, differ very decidedly in different species in the 

 readiness with which they crystallize. Or, a foreign 

 scrum albumin injected into the veins of an animal of 

 different species can not take the place of the correspond- 

 ing albumin of the blood of that species, but acts rather 

 as a poison and is quickly eliminated by the kidneys. 

 Lastly, not unduly to multiply examples of protein 

 specificity, may be cited the precipitins which as you 

 know may in general be used to show the degree of re- 

 lationship of allied forms. For instance, when the 

 blood-serum of one species of animal, let us say man. is 

 injected at intervals into some other species, e. //.. the 

 rabbit, the serum of the latter acquires the property of 

 producing a precipitate in the serum of the first species, 

 man in this case, but not in the serum of other animals 

 unless they are relatively closely related to the first 

 species. Thus the serum taken from rabbit's blood after 

 a series of treatments with human blood will produce 

 precipitation in the blood from any human being. It 

 will produce some, though less, precipitation in the blood 

 of the anthropoid apes, still less in monkeys, and none at 

 all in animals distantly related to man. This implies, 

 manifestly, that the more akin forms are, the more 

 nearly identical are their proteins. And from the evi- 

 dence brought forward in connection with the haemo- 

 globins we have seen that we are perhaps justified in re- 

 garding the differences between the proteins of closely 

 allied forms as ones of molecular configuration rather 

 than of molecular composition or constitution. 



The question may arise in some minds as to whether 



