BACTERIA IN THE AIR AND SOIL 687 



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 

 remembered 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. Experi- 

 ments ^ 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 beings 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 imfavorable cultural conditions. 

 It has been found by some observers,^ however, that, under special con- 

 ditions, non-sporulating bacteria, more especially the typhoid bacillus, 

 may remain aUve in soil for several months. Although these bacteria, 

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

 conditions foimd 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 demonstrating the presence or absence of manure 

 or sewage contamination, has no practical value, since colon bacilli are 

 found in the dejecta of animals. 



Examination of specimens of soil for their numerical bacterial 

 contents is extremely unsatisfactory because the bacteria there found 

 can hardly ever all be cultivated together under one and the same 

 cultural environment. A large number are anaerobic, others again 

 thrive at low temperatures, while again another class may require un- 

 usually high temperatures. When such examinations are made, how- 

 ever, specimens of the soil from the surface layer may be taken in a 

 sterile platinum spoon. When taken from the lower levels, a drill. 



> Petri, Art), a. d. kais. Gesundheitsamt, vii. 



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



