392 V. THE NATURE OF EVOLUTION 



ration, the substance will be removed from the cell as it will become, 

 as a result of the denaturation, a substance foreign to the cell. If the 

 removal of such a substance is accompanied by the destruction of the 

 enzyme systems concerning- the synthesis of the substance, the sub- 

 stance is not only lost but also its synthesis will come to cease, 

 leading to the rejective adaptation of the cell against the agent. 



On the other hand, the inability of producing certain substances 

 may be involved in the corresponding pattern of the protoplasm and 

 accordingly also the gene itself may come to possess the pattern fol- 

 lowing the establishment of a rejective adaptation. If so, the pattern 

 may be transmitted to newly produced cells in so far as the gene 

 retains the pattern thus induced. 



The mechanism of adaptive colour changes, such as those of sala- 

 mander above cited, may be elucidated in this manner. If the struc- 

 ture of a gene is changed so as to reject the visible ray of a certain 

 wave length, under w^hich the cell or the organism is always exposed, 

 the cell or the organism will come to have the colour of the wave 

 length. Thus organisms will become white, when they are exposed 

 to the light of every wave length, since all the visible rays will 

 come to be rejected, whereas they will become black when kept in a 

 dark place as no light will be repulsed. Of course, such a change is 

 valuable as a concealment colouration. In higher animals, hormone 

 systems are amazingly advanced and protoplasm structure changed by 

 environment may be liberated in the forms of hormones to effect the 

 pattern of the protoplasm and also even the genes of the other cells. 

 Thus colour change is usually achieved by special pigment cells called 

 chromatophores the function of which is under the control of hormones. 

 In the case of temporary adaptation as in this case of concealment 

 colouration, only the pattern of the protoplasm may be involved without 

 being accompanied by the corresponding change of the gene. 



The rejective adaptation like the attractive one must be involved 

 in one of the basic characters of the protein. Thus, on the one hand, 

 physical of chemical agents which exert deleterious effect upon organ- 

 isms may tend to cause, as a rule, coagulation of proteins. On the 

 other hand, various polar groups of proteins are likely to disappear 

 when they are coagulated. It appears, therefore, to be a natural result 

 that organisms may adapt themselves to deleterious agents to reject 

 them. In so far as an agent causes the coagulation whereby combining 

 groups may disappear, an organism will achieve a rejecting adaptation 

 to the agent, while if an agent has no action of coagulation, the pro- 

 toplasm may produce the complementary structure in response to the 

 structural influence of the agent with the establishment of the 

 attractive adaptation. 



