(>98 DISTRIBUTION AND HABITAT OF THE BACTERIA. 



energetic processes of oxidation in the soil show us that 

 active life, and in correspondence with that, marked 

 multiplication of bacteria, occurs in it ; but even were 

 the growth very active, the vegetation could only spread 

 extremely slowly over the enormously large surfaces 

 which a porous soil offers, and this mode of spread 

 would not come at all into consideration in the case of 

 pathogenic bacteria. Finally, transport of bacteria can 

 occur in many instances by all sorts of animals which 

 live and move in the soil, for example, by worms, but 

 this can only take place to a very limited extent. On 

 the whole, then, we must regard the bacteria in the soil 

 as more or less fixed in a particular place, and only 

 altering their position slowly and over short distances. 

 Behaviour of The results of the recent investigations as to the 



thepathogemc . . . 5* 



bacteria in the behaviour of pathogenic bacteria in the soil are thus of 

 great importance. We have to ascertain whether the 

 soil can in reality exert a specific influence on patho- 

 genic bacteria, whether such an influence is shown in 

 favouring the growth and the multiplication of the 

 pathogenic bacteria, or whether it affects their preserva- 

 tion and spore formation, or whether, in the third place, 

 it is only the spread of the infective agents from the soil 

 to man which depends on definite conditions of the 

 soil. 



1 Do the From our present knowledge as to the conditions of 



pathogenic ]{f e o f the pathogenic bacteria, it seems very improba- 

 tipiy in the hie that they are able to multiply in the soil. The low 

 temperature in the deeper layers is of itself sufficient 

 to prevent entirely the multiplication of this class of 

 bacteria. In those upper layers, which always or at 

 times show a temperature of at least 16 C., growth of 

 pathogenic bacteria could occur if suitable nutritive sub- 

 stances were present, if there were nothing to hinder 

 the development, and if none of the more rapidly grow- 

 ing saprophytes were present. These conditions, how- 

 ever, are almost never fulfilled under ordinary circum- 

 Unfavourable stances. Numerous experiments by Bolton, Heraeus, 

 d5ionsi V hi the" anc ^ others, have shown most distinctly that even the 

 typhoid bacilli, which are the least fastidious of all 



