BACTERIA IN SOIL 179 



when they burst, some bacteria to be caught in any air cur- 

 rent that is about. The danger is entirely theoretical and 

 there is no evidence that faulty drains produce disease. The 

 constant presence of a disagreeable odor may reduce bodily 

 resistance, that is all. It is, however, more likely that if a 

 householder allow a drain to be faulty the general family 

 hygiene is poor. Bacteria are found in air by filtering a 

 definite quantity of air through cotton or sugar. The former 

 is washed, the latter dissolved in sterile water, and this is 

 examined as outlined under water. 



BACTERIA IN SOIL. 



Microorganisms live in the first few feet of the earth 

 wherever moisture and a small amount of nourishment are 

 found. Pathogenic forms are near the surface, while deeper 

 in pure saprophytes are found. Bacteria are deposited from 

 dust, water, and the dejecta of animals. Pathogenic ones 

 are only to be found where animal life exists, while in unin- 

 habited or untilled lands they probably do not exist at all. 

 The denser the population the more disease-producing kinds 

 are found. Rain will wash away soil and carry with it 

 bacteria into water-courses. This is of great importance 

 where human dejecta are deposited on the ground, but since 

 public health authorities have now control of the disposal 

 of wastes, the soil has become a negligible feature in the 

 transmission of all but a few diseases. 



Typhoid fever epidemics have been known to have such 

 an origin. Typhoid germs can live in soil for many months. 

 Vegetables are easily contaminated, and if eaten raw can 

 transmit the disease. Cholera vibrios have a shorter life 

 in this place. Anthrax bacilli live a long time and cattle are 

 sometimes infected by their pasture. Actinomycosis is well 

 known to spread through a herd because of infected pasture 

 land. The bacteria of soil are found by planting some of it 

 in laboratory media, placing a part at ordinary temperature 

 and another at body temperature. By the latter means the 



