No. 643] 



101 



Thus while the evolutionary process has certainly pro- 

 duced a large number of well-defined series of changes 

 when it is looked at from the morphological point of view, 

 it still remains very probable that such physico-chemical 

 changes as have occurred are not only of a secondary 

 nature, but that they are much less of the character of 

 serial modifications. Indeed, one is tempted to say that 

 in a physico-chemical sense, the variations are distributed 

 in rather a random manner, without any particular indi- 

 cation of a general progressive tendency, such as we seem 

 obliged to think of in studying morphological variation. 



No doubt the evolutionary process has, from time to 

 time, invented new chemical substances and greatly modi- 

 fied colloidal systems. In the total these changes are 

 very numerous and of the utmost importance to the stu- 

 dent of evolution. But progressive change is more par- 

 ticularly a morphological phenomenon and it seems to be 

 almost self-evident that progressive morphological evolu- 

 tion should not be accompanied by the same degree of 

 continuous variation in straight lines in physico-chemical 

 properties. Such a parallelism would, I think, be well 

 nigh unaccountable. However that may be, there is no 

 evidence for it, 



III 



Another consideration wliich makes the theory of or- 

 thogenesis seem very different to a physical chemist from 

 what it must seem to a biologist, is the fact that chemistry 

 tends to deal with individual substances which either 

 exist or do not exist. The case of hemoglobin will illus- 

 trate this point. Hemoglobin is an individual substance 

 of very marked peculiarities. So far as knowTi there are 

 no essential differences between the hemoglobins con- 

 tained in the bloods of different species. It is possible 

 that the known diffen iKcs in (m> sial form depend upon 

 something more than trivial diff. ivnces in the amino 

 acids which make up the inoleeiik-, ])ut this seems unlikely. 

 In any case, it will do no harm to speak of hemoglobin as 



