LECTURE III 



Summary : The Facts of Natural or Spontaneous Variation (concluded) 

 Physiological or Chemical Variation Not always easily detected. 

 May be noticed in all parts of the Body, even between very 

 closely related Forms Exists not only between different Species, 

 but between Varieties of the same Species, Individuals of the same 

 ' Variety, and even different ages of the same Individual Chemical 

 Variation explains Racial Immunity to peculiar Diseases This 

 Chemical or Physiological Variation in some cases of much higher 

 import than any Morphological Variation Chauveau's Experi- 

 ments on Bacillus ant hr ads Physiological Differences between 

 Brown and Green Frog towards Poisons and Heat Tarchanoff's 

 Experiments Variation generally exists at all Ages, in all Groups 

 of Beings, at all Geological Epochs Sudden Variation. 



THERE is a last form of variability to which I wish to 

 call attention, and which has not been enough taken 

 notice of up to the present time. I refer to what I have 

 mentioned under the name of chemical or physiological 

 variability. Under this name I include all facts which 

 indicate a difference in chemical or physiological con- 

 stitution, expressed through differences in the reaction 

 of the organisms towards definite and common external 

 influences. Such chemical variation must certainly 

 exist at the basis of all specific or even racial characters, 



