402 BACTERIOLOGY. 



dwellers in a given locality so as either to 

 diminish or increase it. The inhabitants of 

 any locality are affected not merely by soil, 

 water and air, but also by other and varying 

 conditions of time and place, for example by 

 nourishment, by habitation and by social 

 environment, as we see exemplified in the fact 

 that the development of similar industrial 

 conditions has everywhere brought about a 

 parallel increase of tuberculosis. 



The so-called works of sanitation act, then, 

 by influencing favorably certain social factors. 

 But this influence varies greatly according to 

 the very different weight which the predis- 

 position to disease, and the conditions for the 

 conveyance of the disease and disease germs 

 possesses in the various infectious diseases. 

 Whatever the theory of the matter may be, 

 the spirit is as little affected by our interpre- 

 tation as is the spirit of the law by craftily 

 constructed paragraphs. I must hark back 

 again to the multiplicity of the phenomena 

 involved ; in this chain three links, to keep to 

 my comparison, are of special importance. 

 One of them has been viewed by Pettenkofer, 

 and another by Koch in a one-sided way, but 

 the three together have been sufficiently con- 

 sidered by no one. 



If we remember that in practice, we estimate 



