700 DISTRIBUTION AND HABITAT OF THE BACTERIA. 



that here and there degrees of uncleanness of the soil 

 may he found which permit a short-lived and local mul- 

 tiplication ; but on the whole such a property of the 

 soil is exceptional, even under the conditions employed 

 in laboratory work.. And these conditions are in so far 

 very much more favourable for the multiplication of the 

 pathogenic bacteria than are the natural ones, because 

 in them earth which has been previously sterilised at 

 100 C., and freed from other bacteria, and air not con- 

 taining carbonic acid, are always employed. In reality the 

 concurrence of the saprophytes which find their most 

 favourable conditions for existence in the soil, and also 

 the accumulation of carbonic acid, are in a very marked 

 degree unfavourable for multiplication of the pathogenic 

 bacteria. 



Multiplication Hence it appears to be of relatively little importance 

 veryexcep- ^ or *he question of the multiplication of pathogenic 

 tionally even bacteria in the soil, whether the latter is more or less 

 soil. contaminated, that is to say, impregnated with excreta. 



Possibly greater or less contamination may lead to a 

 certain fluctuation in the prevalent species of bacteria, 

 but all of these belong to the category of the obligatory 

 saprophytes, and leave no room for the facultative 

 parasites which are much more particular as to the con- 

 ditions of their life. Without doubt it will at times 

 happen that a pure cultivation of pathogenic bacteria 

 (for example blood from animals suffering from anthrax) 

 reaches the upper layers of the soil along with good 

 nutritive material, and then multiplication of the 

 anthrax bacilli will occur in the soil so impregnated. 

 But this is evidently no special action of the soil, for 

 the same thing might happen on any other substratum. 

 In a similar manner typhoid and cholera bacilli, which 

 pass along with the fresh dejecta into a soil contain- 

 ing bad nutritive materials and numbers of saprophytes, 

 may multiply to a certain extent for a short time at the 

 expense of the nutritive materials contained in the 

 dejecta, in the same manner as would happen under 

 other very different conditions without contact with the 

 soil. Here there is no sort of favouring and specific 



