1014 BACTERIA IN AIR, SOIL, WATER, AMD MILK 



going on in the upper layers. Furthermore, in the deeper layers 

 the conditions of temperature and possibly oxygen supply are not 

 at all favorable for the growth of most pathogenic bacteria. Within 

 a short distance from the surface the temperature of the soil usually 

 sinks below 14 or 15 C.' An interesting series of experiments by 

 Fraenkel 3 have demonstrated this point. This investigator buried 

 freshly inoculated agar and gelatin cultures of cholera spirilla and 

 of typhoid and anthrax bacilli at different levels, and examined 

 them for growth after two weeks had elapsed. The anthrax bacilli 

 hardly ever showed growth at a depth below about two yards, and 

 cholera and typhoid developed colonies at these depths only during 

 the summer months. Under natural conditions it must be remem- 

 bered that, at these levels, suitable nutritive material is not found. 

 A consideration of practical importance in this connection is the 

 possibility of infection by means of buried cadavers. An elaborate 

 series of experiments has been carried out upon this subject in 

 Germany, with results which demonstrate that the danger from the 

 burial of persons dead of infectious diseases was formerly much 

 exaggerated. Experiments 4 usually failed to reveal the presence of 

 cholera and typhoid bacilli within two to three weeks after burial, 

 and tubercle bacilli were never found after three months had elapsed. 

 It was only in the case of sporulating microorganisms, such as the 

 anthrax bacillus, that the living incitants could be found for as 

 long as two years after burial. The dangers of infection of human 

 being through the agency of soil, therefore, are chiefly those arising 

 from the spore-bearing bacteria which are able to remain alive in 

 spite of. the unfavorable cultural conditions. It has been found 

 by some observers, 5 however, that, under special conditions, non- 

 sporulating bacteria, more especially the typhoid bacillus, may 

 remain alive in soil for several months. Although these bacteria, 

 as well as those of cholera, diphtheria, etc., can not proliferate under 

 the conditions found in the soil, the fact that they can remain 

 viable for such prolonged periods in the upper layers suggests the 

 possibility of danger from the use of unwashed vegetables, such as 

 lettuce or radishes or other soil and sewage contaminated food 

 products. The examination of soil for colon bacilli, while demon- 



3 Fraenkel, Zeit. f . Hyg., xi, 1887. 



4 Petri, Arb. a. d. kais. Gesundheitsamt, vii. 



B Firth and Horrocks, Brit. Med. Jour., Sept., 1902. 



