110 TEXT-BOOK OP BACTERIOLOGY. 



tion of our case of cured rabbits these facts may, we think, be util- 

 ized — with a certain degree of caution, of course. It might be sup- 

 posed that the soluble products of the injected erysipelas cocci 

 render a further growth of the anthrax bacilli impossible, or that 

 they possibly destroj- them altogether. Also that the one decom- 

 poses the products of the others already formed and neutralizes 

 their influence; and if such results are not observable in experi- 

 ments made in our laboratories, the reason may be that the excre- 

 tions of the streptococci do not attain their active properties out- 

 side the living organism. 



Lastly, one can suppose, with Emmerich, that the tissue cells 

 exercise a temporary reaction; the power of resistance to anthrax 

 bacUli which nature has given to the ceUs being increased for a 

 short time and thus enabling them to gain the desired ascendency. 



III. EXAMINATION OP INFECTED ANIMALS— METHODS OF IN- 

 OCULATION. 



The pathogenic bacteria are by far the most interesting to us. 

 Wherever and whenever we find micro-organisms, in the human 

 body or in animals, the question always arises whether we have 

 this variety of micro-organisms or not. The answer is often dtfil- 

 cult and must always be according to fixed and definite rules which 

 were first laid down with exactness and precision by Koch many 

 years ago. 



These rules require that a micro-organism, to be recognized as a 

 specific agent in the production of pathological alterations, should 

 fulfil three conditions : 



First, it must be proved to be present in all cases of the disease 

 in question. 



This is a matter of course, and scarcely requires a justification; 

 for if the disease can occur without the bacterium, the latter is not 

 unconditionally necessary and cannot be regarded as specific. 



Second, it must further be present in this disease and in no 

 other, since otherwise it could not produce a special definite action. 

 We often meet with apparent violations of this condition and find 

 bacteria which we regard as specific, in the sense alreadj' explained, 

 and whose occurrence is, nevertheless, not confined to one disease. 

 Such exceptions are, however, explainable by the differences which 

 various kinds of bacteria show according to the place of entrance, 

 the organ they have attacked, the degree of susceptibility in the 

 organism attacked, the degree of virulence which they possess, etc., 

 etc. A careful consideration of all these different factors will suf- 

 fice to guard against errors and false conclusions. 



