VII. THE MECHANISM OF ADAPTATION 391 



established by some combining group present in tlie protoplasm or on 

 the cell surface. In the case of the attractive adaptation, such a com- 

 bining group is strengthened by the adaptation. A sugar or an antigen 

 may combine with bacteria or antibody-producing cells, respectively, 

 through such a combining group to act as a stimulus causing the 

 adaptation ; and after the establishment of the adaptation the combin- 

 ing group will be reinforced so much that the group, if liberated 

 from the protoplasm, can act as the enzyme or the antibody, respecti- 

 vely. Also a virus can affect a cell because a combining group directed 

 to the virus may be present on the cell surface, and after the infection 

 the protoplasm structure will become complementary to that of the 

 virus ; as a consequence the cell will combine readily with the virus 

 but without being exerted any injurious effect by the latter. Thus 

 the cell will become. immune to the virus as a result of the attractive 

 adaptation. 



However, such a complementary structure may fail sometimes to be 

 produced following a virus infection as in the case of influenza virus 

 affecting red-blood corpuscles, presumably because of the character of 

 the cells unable to produce the pattern completely complementary to 

 that of the virus. The failure in the production of complementary 

 structure may give rise to only the disturbance in the protoplasm 

 structure by the virus, leading to a type of coagulation of the protein, 

 whereby various free polar forces including the combining group for 

 the virus will be lost. As a natural result of this disappearance of 

 the combining group, the virus will be released from the cell and at 

 the same time the cell will become immune to the virus, thus the 

 rejective adaptation being established. 



For instance, when a virus such as that of influenza combines 

 with a red cell, only a structural disturbance will result, causing the 

 disapearance of the combining group, because the red cell is not sus- 

 ceptible to the virus and so cannot reproduce the virus, that is, the 

 cell cannot form the complementary pattern so as to establish the 

 attractive adaptation. As a consequence the cell may acquire the pro- 

 perty to reject the virus and the virus will be released from the cell. 

 If such a change is given rise to by an agent other than a virus, 

 it may be said that the cell is adapted itself to the agent not to be com- 

 bined by it. The mechanism by which an enzyme can liberate from a 

 molecule of a changed substrate to affect another unchanged substrate 

 is elucidated in a similar way as discussed in chapter V, in Part IV. 



In the majority of cases, a number of combining groups directed 

 respectively to each group of agents may be involved in some consti- 

 tuents ' present on the cell surface. If such a constituent combines 

 with an agent to be disturbed in its structure and undergoes denatu- 



