608 A MANUAL OF BACTERIOLOGY 



After sterilisation the tube is ready for use. The wool plug is 

 removed from the mouth and a measured volume of air is aspirated 

 through the layer of powdered sugar by means of a small hand 

 air-pump, the volume of air being measured by the displacement 

 of water in a flask. Having taken the sample (5 to 20 litres), the 

 wool plug is replaced in the neck. The powdered sugar is then 

 shaken down into the wide part of the tube (A), and 15 c.c. of melted 

 sterile nutrient gelatin are poured in. The powdered sugar readily 

 dissolves in the melted gelatin, and when solution is complete a 

 roll-culture is made in the tube, just as in Esmarch's method (p. 83). 

 The tube is then placed in an incubator at 20 C., and the colonies 

 are allowed to develop. 



In both Frankland's and Sedgwick and Tucker's methods the 

 sugar, after powdering and sifting and before introducing into the 

 tubes, should be thoroughly dried by keeping in the warm incubator 

 for several days ith occasional stirring. Unless this be done, the 

 sugar is apt to cake and discolour during sterilisation. 



Soil 



The upper layers of soil contain large numbers of organisms, 

 chiefly bacilli. The species are very varied ; among pathogenic 

 ones may be named the bacillus of tetanus and of malignant oedema. 

 The B. mycoides is very abundant, and the varieties of Proteus, 

 the hay and potato bacilli, are common, while the nitrifying forms 

 are of course present, but do not develop on ordinary media. 



Below five or six feet aerobic organisms become scanty, but the 

 anaerobic and thermophilic ones are still met with. The number 

 of organisms present in soil is variable, from 200,000 to 45,000,000 

 in ordinary earth, while in dirty and busy streets there may be as 

 many as 1,000,000,000 per grm. According to Houston, unculti- 

 vated sandy soil averages 100,000, garden soil 1,500,000, and sewage 

 polluted 115,000,000 per grm. 



Houston * found that in virgin soils the B. coli, B. Welchii, and 

 streptococci are practically absent, but that in soils polluted with 

 animal excrement by manuring or otherwise the spores of B. Welchii 

 are present in great abundance, also B. coli and streptococci if the 

 pollution be of recent date. 



The length of time pathogenic bacteria retain their vitality in 

 buried corpses has been the subject of experiment by Losener, 2 



1 Rep. Med. Off. Loc. Gov. Board for 1889-1900. 



2 Centr.f. Bakt. (V Q Abt.), xx, 1896, p. 454. 



