230 BACTERIA. 



medium, the virulence of the organism, or its power of 

 growing in tissues, was distinctly diminished — i.e., the 

 organism was in a condition to be much more readily de- 

 stroyed by the cells of the animal body, which appeared to 

 keep the upper hand throughout the struggle, very few of the 

 cells being destroyed, as is the case when virulent tubercle is 

 used, where although a number of the tubercle bacilli are un- 

 doubtedly destroyed, the degeneration of the proliferated cells 

 is so extensive that caseous nodules are formed, and the typical 

 appearance of caseating tubercle are presented in the inocu- 

 lated area. The second factor, though equally important, and 

 though recognized indirectly by all physicians, could not put 

 itself so fully in evidence as the first, and it was only ^ter 

 Metschnikoff had made his beautiful observations on the daph- 

 nia and on the separating tail of the tadpole and the phagocyte 

 action of certain cells in these processes, that any direct evi- 

 dence of the bearing of the activity of the cells of the tissues 

 of the body on the destruction of micro-organisms within the 

 body could be definitely adduced. Then, indeed, began the 

 narration of the history of the battle between the cells and 

 the bacilli. If the bacilli were weak, or were present in small 

 numbers only, the cells were invariably the victors ; if the 

 cells were degenerated, or were badly nourished, or if their 

 vitality was low, the bacilli proved themselves the more 

 powerful. How these results were brought about soon 

 became the subject of most violent controversy, and in the 

 controversy thus raised explanations of facts that had hither- 

 to puzzled scientific workers were projected and forced home. 

 Let us here, however, examine only those facts that appear 

 to have a special bearing on the subject of tuberculosis. 

 A perfectly healthy individual, placed under favourable con- 

 ditions as regards food, fresh air, and exercise, is never 

 attacked successfully by tubercle bacilli, the active, vigorous 

 tissue cells being perfectly competent to destroy any bacilli 

 that may make their way into the lungs, the pharynx, or the 

 intestine ; whilst even in cases of direct inoculation into a 

 wound, if the wound heals rapidly, no tubercular process 

 may result, the tubercle bacilli, as we have said, being 

 destroyed by the cells. It may be, indeed, that certain 

 secretions of the cells — i.e.., those substances that bear the 

 same relation to the connective tissue cells that an enzyme 

 bears to the yeast-cells — also exert a deleterious action on the 



