234 THE CAUSATION OF DISEASE. 



must be tending towards a complete adaptation, for how count- 

 less is the number which are yearly thus destroyed ! And that 

 such a complete adaptation would actually occur, I doubt not, 

 were the virus constant in its properties during several genera- 

 tions of men. Since it is not, perfect adaptation is impossible ; 

 but there is a continual struggle towards it, and in this way a 

 certain level of adaptation is maintained. 



Next to instability of E, the growth of hygienic science is the 

 most important check to the process. Take the case of typhoid 

 fever : a number of individuals congregate, the typhoid germ 

 comes into being, and disease results.* Forthwith the process 

 of adaptation is set on foot, but the reasoning power of man at 

 once steps in to check its progress. He searches out the cause 

 of typhoid, and directs his efforts to its destruction. A perfect 

 adaptation to a typhoidal E, even were it possible, would 

 involve a terrible sacrifice of life, so that man wisely deter- 

 mines to control the E ; that is to say, he adapts the E to 

 himself, instead of allowing himself, or rather his race, to be 

 adapted to the E during the long course of ages. 



There is nothing absurd in the supposition that man could 

 ultimately become adapted to a typhoidal E, provided only its 

 fixity could be guaranteed. The yellow fever, so fatal to the white 

 man, rarely or never attacks coloured races. This poison, there- 

 fore, does not constitute a necessarily fatal form of E. Now I 

 do not contend that the coloured races have adapted themselves 

 to the yellow fever virus by a process of natural selection. 

 Whether or not this is so, I do not pretend to say : so far as 

 I know, there is no evidence in favour of it. I merely wish to 

 emphasize the fact that a poison, probably generated by the 



* I confess I am one of those who believe in the de novo origin of specific 

 fevers. It may be regarded as proved that these fevers are due to " germs," 

 but many hold the theory of spontaneous generation to be untenable. Sup- 

 posing, then, spontaneous generation never to occur, and the specific fevers 

 to be due to germs, how can we account for their de novo origin ? In a very 

 simple way. We have only to suppose the de novo assumption by non-patho- 

 genic germs of pathogenic properties, such assumption resulting from 

 peculiarities of germ E ; in which case, looking on spontaneous generation as 

 an impossibility (which I for one am far from doing, for at the most we can 

 but prove that this never occurs in a test tube), and on the specific fevers as 

 due to specific germs, we can yet readily account for their de novo origin. 

 Vide " The Evolution of Morbid Germs : " K. W. Millican. 



