390 V. THE NATURE OF EVOLUTION 



tures are in the majority of cases favourable for the organism having- 

 been able to continue their existence up to the present. 



Now, if a factor causing such an adaptation is a chemical agent 

 having a definite structure, the organism has to be changed to become 

 complementary in their structural pattern to the chemical agent in 

 order to become adapted to the latter, as the adapted structure of the 

 organism must be the structure completely complementary to that of 

 the agent. When such an adaptation is accomplished, the organism 

 can readily combine with the agent through the complementary pattern 

 but without being exerted any influences. As a good example of this 

 type of adaptation will be mentioned the so-called adaptive enzymes. 



A certain strain of colon bacteria will gain the faculty to utilize 

 lactose when cultivated in the medium containing this sugar. It is 

 believed that in such a case an adaptive enzyme to ferment the sugar 

 is produced. In order to utilize the sugar, the bacteria are to combine 

 easily with it, and the combination will be achieved by the production, 

 or rather reinforcement, of the combining group. The appearance in the 

 bacteria of the structure complementary to that of the substrate as a 

 result of the adaptation must account for the reinforcement of the 

 combining group. The bacteria cannot utilize the sugar presum.ably 

 because they are not provided with the strong combining group for 

 the sugar. In like manner, antibody production is also regarded as 

 this type of adaptation of certain cells against the antigen. Again 

 virus is produced by a virus because the complementary structure is 

 formed in the protoplasm. Thus it may be said that virus-formation 

 is also involved in this type of adaptation. The production of such 

 complementary structure in response to chemical structures of the 

 stimulants appears to be based upon the general and essential charac- 

 ter of the protoplasm. Viruses, antibodies, and adaptive enzymes are 

 nothing but the structures freed from the protoplasm thus adapted to 

 respective stimulants. 



Anyhow, if a complementary structure given rise to in the proto- 

 plasm of a cell or of an organism by a certain agent is transferred to 

 the gene, or the structure is raised directly in the gene, then the 

 cell or the organism can be regarded as having adapted itself to the 

 agent with the acquisition of the property to utilize the agent. This 

 type of adaptation may be designated as attractive adaptation, as 

 attractive or combining structure is to be strengthened as a result 

 of the adaptation. However, in addition to this, there seems to be 

 another type which may be called rejective adaptation. Next a mention 

 will be made of this type of adaptation. 



An agent, in order to act as a stimulus on an organism, must be 

 received by the protoplasm of the organism. The reception may be 



