706 DISTRIBUTION AND HABITAT OF THE BACTERIA. 



Food. 



By animal?. 



Digging. 



Seasonal 

 influences on 

 their spread 

 due to the 

 moisture of 

 the ground. 



Behaviour of 

 the water in 

 the soil. 



face if it increases in amount, and also when fissures 

 and cracks open a communication between the contents 

 of cesspools and the ground water used in houses, it will 

 occasionally happen that the bacteria poured into the 

 soil again return to man and to dwellings. 



3. Articles of food which grow in the soil (potatoes, 

 turnips, roots, &c.) carry particles of earth adhering to 

 them, and large numbers of bacteria from the upper 

 layers of the soil, into dwellings, kitchens, kitchen uten- 

 sils, towels, &c., and thus ultimately to other kinds of 

 food. 



4. Men and animals who come in any way in contact 

 with the soil, implements which are employed in culti- 

 vation, &c., can in a similar manner aid in the transport 

 of the bacteria from the soil to the domestic economy. 



5. By digging the soil and laying bare the deeper 

 layers which may contain bacteria, while at the same 

 time dry winds prevail, numbers of pathogenic bacteria 

 may be detached which have reached the soil from de- 

 fective cesspools, or at a former time from the surface, 

 but which have been withdrawn from contact with the 

 outer air by being covered with new layers of soil. It 

 is possible that we may in this way explain the fre- 

 quently suggested connection between typhoid epide- 

 mics and digging up the soil of streets. 



As a matter of fact it is evident that these various 

 modes of transport of the pathogenic bacteria of the soil 

 do not come equally into action in every soil and at every 

 season, but that local and seasonal causes of variation 

 exist, and favour or hinder one or other mode of trans- 

 port. 



The seasonal influences are most distinctly seen in 

 the first and most widespread mode of transport, viz., 

 the spread through the air ; and this is due to the 

 varying degrees of moisture of the upper layers of the 

 soil. 



As to the important conditions of the moisture of the soil 

 in relation to this point we have obtained clearer information 

 by Hofmann's investigations.* In porous soil we have to 



Arckiv f. Hygiene, vols. i. and ii., Part 2. 



