No. 554] ADAPTATION AND THE PHYSIOLOGIST 103 



be so? Pigment is itself the result of a long and complex 

 series of changes. If a given cell produces no pigment it 

 is perfectly certain that its other chemical processes 

 are to some degree modified also, so that these other 

 things vary also. If this cell is changed so that it pro- 

 duces no pigment, then since it is the logical result of a 

 long series of changes in the developing organism, those 

 changes must have been different in animals producing 

 pigment and no pigment. But this means, since each 

 process in the early stage of development influences a 

 multitude of processes in the final change, that there must 

 be a host of differences correlated with the pigment 

 change. As a matter of fact, Darwin long ago pointed out 

 that pigment production was apparently correlated with 

 other factors; particularly with vital resistance, a fact 

 repeatedly mentioned to the writer, also by Whitman as 

 a result of his experiments in pigeon breeding. Darwin 

 cites the case of the Virginia pigs of which only the black 

 ones could eat a poisonous root without losing their hoofs ; 

 and Whitman told me that always birds deficient in pig- 

 ment were also somewhat deficient in other characters 

 and were weaker. 



The essential unity* of the organism is not only fatal to 

 the whole theory of unit characters, but it is an insuper- 

 able objection to the theory that evolution has been by 

 jumps. The organism is a finely adjusted mechanism of 

 a very complex kind ; it seems impossible to a physiolo- 

 gist that one can cause a sudden large change in any part 

 of it and have it continue to function ; it is as incredible 

 as if one should remove one of the wheels of a watch, 

 replace it by a larger one, and expect the watch to con- 

 tinue to run. Such a simple matter as the replacement 

 of urea by uric acid as an excretion, a change which the 

 reptiles introduced in their differentiation from the am- 

 phibia, a change which might conceivably be brought 

 about by the dropping out of a uricolytic enzyme, could 

 not take place suddenly. The kidneys and all other organs 

 of the body would need to be adjusted to this change. 



