322 Problems of Organic Adaptation 



not in general be synthesized by human intelligence. Other 

 chemical substances of unknown composition but of the most 

 vital importance as accessories to food are known as vita- 

 mins. They are produced only by certain cells and tissues of 

 plants and animals, and they have never yet been analyzed 

 or synthesized. 



These are only a few of the many unique and wonderful 

 chemical secrets which protoplasm has discovered but which 

 are as yet largely beyond human comprehension. How did 

 lowly plants and animals ever discover such subtle secrets 

 of chemistry, which intelligent man is only coming to ap- 

 preciate and which he cannot yet artificially duplicate? 



II. INDIVIDUAL, ACQUIRED, OR CONTINGENT 

 ADAPTATIONS 



As contrasted with such racial or inherited adaptations, 

 there is a whole class of fitnesses which may be known as 

 individual, acquired, or contingent. These are adaptations 

 which arise in response to particular stimuli; they are not 

 inherited, as the structure of the eye is, for example, which 

 develops in the dark as well as in the light, and which is 

 fully formed before it is put to the use for which it is fitted, 

 but they are acquired in that they arise in each individual 

 in response to particular external conditions, and they are 

 contingent in that they may or may not appear, depending 

 upon whether the appropriate stimulus is present or not. 



Among these individual adaptations, or useful responses 

 to stimuli, may be listed the following classes : 



Stimulus Beneficial Response 



Increased light Increased pigmentation 



Increased friction Increased thickness of epidermis 



Increased use Increased size or strength 



Unusual foods Appropriate digestive fluids 



