692 DISTRIBUTION AND HABITAT OF THE BACTERIA. 



factor in the occurrence of epidemic diseases. The 

 connection proved by statistics to exist between the varia- 

 tions in the mortality from typhoid fever in Munich and 

 the variations in the level of the ground water furnished 

 the chief argument for the view that something took place 

 in the soil which exercised an important influence on 

 Pcttoukofer's the spread of a number of infective diseases. The 

 interesting results of that statistical observation leave it 

 llowever > in tlie first P lace > doubtful whether the alteration 

 tive bacteria, in the soil, as shown by variations in the ground water, 

 exercise any influence on the development of the infective 

 germs ; or whether it is only of special importance for 

 the transport of the germs present in soil to man ; or 

 whether, in the third place, there is a direct connection 

 between the conditions of the soil and the infective 

 germs, or an indirect one in this way, that the apparently 

 predisposing condition of the soil and the spread of the 

 epidemics must be referred to a third causal factor 

 common to both. Further, the question arises, sup- 

 posing that the soil exerts some direct influence on one 

 or several of the infective agents, whether this influence 

 must be regarded as absolutely necessary for the epidemic 

 spread of the diseases in question, so that a necessary and 

 specific role must be assigned to the soil ; or whether 

 the spread of the same disease may not frequently occur 

 in other ways without any connection with the soil ? 



The decision of these questions is evidently only 

 possible when we obtain a more accurate knowledge of 

 the pathogenic agents, of their vital characters, and of 

 their mode of spread ; before we possessed any know- 

 ledge of this kind we could only form hypotheses as to 

 the more intimate connection between the soil and in- 

 fective diseases. 



View as to a Pettenkofer and his followers formerly sought to show 

 fluoncc of the *kat ^ was P r bable that the soil exercised a peculiar 

 soil on the and definite influence on the development of the infective 



development ., . , . 



and spread of germs as well as on their transport to man ; a porous 



' tlvc soil infiltrated with waste organic materials and moistened 



from time to time was supposed to be indispensable 



for the development, and, so to speak, ripening of the 



