TISSUE-SELECTION IN THE GENESIS OF DISEASE. 8 39 



does not deprive them of their original power of attacking degenerate 

 tissue. It is simply an additional power, rendering them more potent 

 when Drought into contact with tissue possessing certain character- 

 istics. These characteristics of the tissue originally attacked may 

 determine the character of the action of the germs on other tissues, 

 and thus enable us to recognize a relationship in the morbid influences 

 at work in different tissue as, for example, in syphilitic disease. If 

 it is a fact that the tissue originally attacked modifies the constitution 

 of the germs, it is surely more reasonable to suppose that the special 

 characteristics thus impressed upon the germs are those which give 

 the family likeness to the descendants of these germs, rather than to 

 suppose that this morbid family likeness exists in the germs before ever 

 they have been brought into contact with any form of degenerate 

 tissue. In other words, may not a bacterion, pure and simple, by 

 being brought into contact with some form of degenerate tissue, 

 acquire or give rise to other bacteria which possess certain charac- 

 teristics which we recognize as being those of special disease, and 

 that those characteristics enable them to excite a similar form of 

 disease in the new nidus ? It is also conceivable that as different 

 diseases are more or less wide-spread or of older standing, so the germs 

 given off from tissues affected by these diseases will have more and 

 more power of affecting tissues less and less degenerate, even to the 

 point of a possible condition of actual health. So, for example, the 

 germs of scarlet fever or measles have actually acquired great power 

 over the tissue which they primarily affect ; whereas in the case of 

 tuberculosis it is more than doubtful whether the actual presence of a 

 tubercular condition of degeneration in the tissue, to a definite extent, 

 is not necessary before the germs can find a suitable nidus in that tissue. 

 Of course, germs derived from a tubercular origin will have more in- 

 fluence over tissue which is not so much affected than germs which 

 have not such tubercular origin. It is, in fact, simply a matter of 

 degree of degeneracy. May it not be this which enables persons free 

 from tubercular taint to brave the assaults of germs be they ever so 

 virulent ? 



The above are only one or two examples showing the different 

 powers possessed by germs derived from the different forms of disease. 

 The list of examples might be almost indefinitely prolonged. But the 

 result would only be to show that different diseases have different 

 powers of affecting the animal body, a fact already well known. It is 

 the design of this paper to show that possibly these powers have been 

 acquired by the action of some form of natural selection, here proposi- 

 tionally called " tissue-selection," on the germs which inhabit the air 

 we breathe and the water we drink, such action in the course of long " 

 ages having given rise to germs possessing special powers, and being 

 now apparently unrelated to each other in any way. The intermediate 

 steps between a simple germ and such a highly modified one, as, for 



