SPECIAL EXAMINATIONS 365 



BACTERIOLOGICAL EXAMINATION OF SOIL. 



A quantity of soil may be collected in a platinum or 

 metal spoon, or in a sterile tin trough, or by a Fraenkel's 

 borer. A definite quantity is ground up in a sterile mortar 

 and then mixed with known quantities of sterile water. 

 Cultures are then made from definite quantities of these 

 dilutions, and the number of B. coli, of streptococci, and 

 of spores of B. enteritidis sporogenes, are determined and 

 returned as so many per gramme of the original soil. 

 Houston found 100,000 (of all bacteria) per grm. in sandy 

 uncultivated soil, and 1,500,000 per grm. in garden soil. 

 Spores are determined by adding 1 c.c. of a dilution to- 

 10 c.c. of gelatin ; heat to 8o C. for ten minutes to destroy 

 non-sporing bacteria, plate, incubate, and count as late as 

 liquefaction (if present) will allow. The examination 

 for specific pathogenic bacteria is carried out by injecting 

 animals subcutaneously, with some of the material or a 

 dilution of it in normal saline (o-8 per cent). 



Organisms Found. The bacteria found in soil are : 

 (a.) Putrefactive organisms 



B. mycoides (earth bacillus). 

 B. subtilis (hay bacillus). 

 B. megatherium. 

 (b.) Nitrifying organisms or nodule bacteria 

 Nitroso-bacteria, or nitrite formers. 

 Nitro-bacteria or nitrate formers. 

 (c.) Pathogenic organisms 

 Bacillus of tetanus. 



,, of malignant oedema. 

 of quarter evil. 



enteritidis sporogenes. 



DUST, SEWAGE AND SEWAGE EFFLUENTS, 

 AND EXCREMENTAL MATTERS. 



These are examined on similar principles, except that a 

 dry solid, like dust, may be weighed out, crushed in a sterile 

 mortar, and made into a primary dilution with distilled 

 water. Gordon found that in the dust collected at air inlet 

 at House of Commons there were under 10 bacteria per 



