138 THE DIFFERENT TYPES OF IMMUNITY 



if from this a transplant is made to rat B a tumor develops as in 

 rat A. To explain this peculiar behavior Ehrlich suggested that 

 some specific substance which we may call X, and which is supposedly 

 found only in the body of the mouse, and which is essential to 

 the growth of the mouse cancer, is transferred to rat A when the 

 first transplantation is made. As long as a supply of this substance 

 is available the cancer cell can multiply and make use of the usual 

 foodstuffs of the organism of the rat. As soon as this is exhausted, 

 however, further development is not possible, and if at this time 

 rat B is inoculated no growths occurs because the specific growth 

 stuff X is absent. If a transplant be made back to a mouse, how- 

 ever, X is again supplied and a transfer to rat B will then again 

 lead to successful growth until X is again used up. The immunity 

 of the rat to the mouse cancer is thus evidently dependent upon an 

 athrepsia, i. e., an absence of a specific substance which is essential 

 to the growth of the mouse tumor cells. This concept of a certain 

 form of tumor immunity is theoretically, at least, applicable to certain 

 types of antibacterial immunity also, even though the experimental 

 basis for such an assumption has not yet been supplied. 



We know, of course, that certain organisms can be grown outside 

 of the body only if certain special substances are supplied, and that 

 in their absence growth ceases. A familiar example is furnished 

 by the influenza bacillus. If this is transplanted from hemorrhagic 

 sputum to ordinary culture media a certain amount of growth is 

 at first obtained, but unless hemoglobin is artificially supplied to 

 the subcultures the organism soon dies out. We may accordingly 

 imagine that certain animals are immune to infection with certain 

 organisms because the macroorganism does not supply all those 

 substances which are essential to the growth of the microorganism, 

 but, as just stated, we do not as yet know what those substances 

 are, and we do not know against what organisms an athreptic 

 immunity exists. We merely recognize the possibility and must 

 reckon with it in our discussion of the subject. 



Antiaggressin Immunity. Another factor which must be considered 

 in connection with the question regarding the mechanism, which 

 is operative in the production of antibacterial immunity, is the 

 possibility that the organism, which has found its way into the 

 body, may be devoid of all aggressivity, and might hence fall an 

 easy prey to the normal defensive mechanism of the macroorganism. 



