BACTERIA AND DISEASE 267 



Then comes in a third category, a long list of diseases, such 

 as scarlet fever, small-pox, rabies, and others too numerous 

 to mention, in which the nature of the causal agent is still 

 unknown. Hence it must not be supposed that every dis- 

 ease has its germ, and without a germ there is no disease. 

 Such universal assertions, though not uncommonly heard, 

 are devoid of accuracy. 



In the production of bacterial disease there are two factors. 

 First, there is the body tissue of the individual; secondly, 

 there is the specific organism. 



Whatever may be said hereinafter with regard to the 

 power of micro-organisms to cause disease, we must under- 

 stand one cardinal point, namely, that bacteria are never 

 more than causes, for the nature of disease depends upon the 

 behaviour of the organs or tissues ^vith which the bacteria or 

 their products meet (Virchow). Fortunately for a clear con- 

 ception of what " organs and tissues " mean, these have 

 been reduced to a common denominator, the cell. Every 

 living organism, of whatever size or kind, and every organ 

 and tissue in that living organism, contains and consists of 

 cells. Further, these cells are composed of organic chemical 

 substances which are not themselves alive, but the mechani- 

 cal arrangement of which determines the direction and power 

 of their organic activity and of their resistance to the specific 

 agents of disease. With these facts clearly before us, we 

 may hope to gain some insight into the reasons for depart- 

 ure from health. 



The normal living tissues have an inimical effect upon 

 bacteria. Saprophytic bacteria of various kinds are normally 

 present on exposed surfaces of skin or mucous membrane. 

 Tissues also which are dead or depressed in vitality from 

 injury or previous disease, but which are still in contact 

 with the tissues, afford an excellent nidus for the growth of 

 bacteria. Still these have not the power, unless specific, to 

 thrive in the normal living tissue. It has been definitely 



