704 DISTRIBUTION AND HABITAT OF THE BACTERIA. 



Local and as yet by no means proved, power of the soil of preserv- 



seasonal 



differences in nig pathogenic bacteria is subject to local and seasonal 



Seso3to variations; and whether these variations might suffice 



bacteria * ex P^ n tne ^ oca ^ an ^ seasonal differences in the dis- 



tribution of epidemic diseases as understood by Petten- 



kofer ? 



Although we have as yet no experimental proof of 

 such a view, it is probable that certain local and seasonal 

 differences in the preserving power of the soil do in fact 

 exist. Thus compact rock, which does not permit the 

 entrance of fluids and bacteria, would be out of the 

 question as a means of preservation. Further, the va- 

 rious forms of porous soil would show quantitative 

 differences according to the size of the particles and the 

 degree of porosity. Possibly also the greater or less con- 

 tamination of the soil is of influence, but only in so far 

 that if the soil contains a large quantity of saprophytes 

 and of nutritive materials, it will be less suitable for the 

 preservation of pathogenic bacteria. 



As regards time also, certain variations may occur ; 

 more especially it is conceivable that a very moist soil 

 presents more the conditions of a fluid, and prevents the 

 rapid distribution and fixation of the bacterial masses 

 which are necessary for their preservation, while the 

 action of the air which, is present in the pores of a soil 

 only partially moistened does not occur, and thus preser- 

 vation is prevented. As excessive moistening of the 

 upper layers of the soil is generally accompanied by a 

 high level of the ground water, the sinking of the ground 

 water may frequently indicate increased suitability of the 

 soil for the preservation of pathogenic bacteria. 

 The preserva- But in spite of the possible existence of these local 

 all( l seasona l variations, the preserving power of the soil 



n 

 the soil is, would not be in the slightest degree sufficient to exert 



however, not . , , .-..,. 



necessary for an exclusive influence on the spread of epidemic dis- 

 eases. For we cannot assume with regard to any species 

 of bacterium that the condition of preservation in which 

 it is present in the soil is at all necessary to fit it for 

 being transmitted to other individuals ; on the contrary, 

 all infective agents are without doubt capable of causing 



