OUR FUTURE COURSE 205 



If the human epidermis is subjected to the rays 

 of the sun it becomes pigmented. If the stimulus 

 is continued the pigment increases, and finally 

 the maximum power of the body to form pigment 

 is expressed or an effective protection against the 

 inciting stimulus is attained. The action is prob- 

 ably cumulative. In the case of tolerance for nar- 

 cotics the cumulative nature of the action is even 

 more evident, for tolerance may be built up by 

 gradually increasing the dosage, to a point which 

 is not found in untreated individuals, and a return 

 to normal must be accomplished in the same way, 

 by gradually decreasing the dosage. According 

 to Wells ^ tolerance for morphine and alcohol must 

 be, in part at least, due to ''a certain refractoriness 

 or cellular immunity," in addition to any possible 

 power to destroy the toxic substance. Whatever 

 may be the mechanism of this tolerance, which is 

 not definitely understood, it indicates a cumula- 

 tive acquisition of a quality present to a much 

 smaller degree in the initial state of the individual. 



That the response of the heritage is invariably 

 cumulative in individual response to environment 

 cannot be said with certainty. Information on this 

 subject is inadequate. Nevertheless the available 

 facts point to this probability. While with-holding 

 dogmatic assertion on the question, we may work 

 with confidence on the tentative conclusion that 



3 The Chemical Aspects of Immunity, Ch. XII, 1925. 



