W. Henry Kesteven

“ In the relationship of the germs and the degenerate tissue, it is plain that in one sense the germs are the active, and the tissue the passive, elements. But, looked at from the tissue point of view, it will also appear that this passive condition possesses considerable indirect influence on the germs; that, indeed, "passive" is hardly the word to express the action which must largely modify their constitution. It would be impossible for the germs to live, to grow, to multiply on a certain tissue without becoming imbued with certain characteristics of that tissue. ”

“ 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. ”

“ Among these is sexual selection, and, taking a broad view, we may also include selection by man. In order, then, to the attainment of greater exactness, may we not give a name to that form of natural selection which has been potent in bringing about the variations in the characteristics of those germs to which the differences in the forms of disease are due? Such a term may be found, I would suggest, in "tissue-selection," as indicating the special means whereby the constitution of the germs has been modified. ”

“ Now, the one characteristic of the tissue which most strikes our attention is its degeneracy, and this degeneracy must exert its influence on the organisms which depend upon it for existence, so that in the thus derived organisms we have the germ vitality and function, plus a certain amount of degenerate tissue characteristic. ”

“ 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 characteristics 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? ”

“ The most important of these, or the one that most interests us in the present connection, is the law of natural selection; and it must be that germs, in common with other forms of life, are under the influence of this law in some shape. Natural selection is a general term which embraces all other modes of selection, or provision for the "survival of the fittest." ”

“ Germs may still exist which have only the power of exciting a simple inflammation in any degenerate tissue. Others, a step more advanced, are found, whose action is more potent, which have attractions for the one special tissue in which they have been bred ”

“ 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. ”

“ This power or, rather, increase of power—in other words, further variation in constitution—thus displayed is only to be accounted for by the supposition that its acquisition is secondary to the act of establishment, and that it is brought about by means of the blood itself receiving some of the germs and conveying them to some other tissue, on which, in virtue of its degeneracy, and possibly of a further modification, they have themselves received from the blood, they are enabled to effect a settlement. ”

“ At the same time it can not be considered absolutely obnoxious, as it is the means which favors their locomotion in the atmosphere. Putting aside, for the mean while, the thermometric and atmospheric conditions, we shall see that the condition which most concerns us is that of a favorable nidus. ”