EXAMINATION OF SOIL 609 



who injected cultures into the bodies of pigs, which were then 

 wrapped in linen, placed in wooden coffins, and buried. The 

 conclusions he arrived at were that, provided the soil has good 

 filtering properties, there is practically no chance of the dissemina- 

 tion of a virus. 



Klein, 1 experimenting with the bacilli of diphtheria, cholera, 

 plague, typhoid fever, etc., also found that the vitality and infective 

 power of these organisms passed away in a comparatively short 

 time, in most cases within a month. 



On the survival of the typhoid and cholera organisms in soil 

 see also pp. 363 and 437 respectively. 



Examination of Soil 



The bacteria in the soil may be examined by adding traces of the 

 soil to sterile nutrient broth, thoroughly crushing and soaking it, 

 and then making plate or roll cultures, aerobic and anaerobic. 



To make anything like an accurate quantitative examination is 

 almost impossible. Weighed amounts of the soil, after thorough 

 pulverisation in an agate mortar, may be introduced into sterile 

 test-tubes and thoroughly exhausted by repeated washing with 

 sterile water or broth, plate cultivations being made with the 



Various forms of boring apparatus have been devised for with- 

 drawing soil from different depths. 



Sewage 2 



Sewage is exceptionally rich in organisms, but the numbers present 

 are variable. Jordan in Massachusetts found an average of 708,000 

 per cubic centimetre. Laws and Andrewes found from 905,000 

 to 11,216,000, the latter being the highest number obtained. The 

 number of organisms naturally varies at different seasons and 

 with the amount of dilution. The organisms present are very 

 varied, but moulds, yeasts, and sarcinse only occasionally occur. 

 A few micrococci are met with and streptococci are present in 

 considerable numbers, at least 1000 per c.c., but bacilli, especially 

 liquefying forms, largely predominate. The commonest species 



1 Rep. Med. Off. Loc. Gov. Board for 1898-99, p. 344. 



2 See various Reports to the London County Council by Clowes, 

 Houston, Laws and Andrewes ; Klein, Houston, Reps. Med. Off. Loc. 

 Gov. Board for 1897-1904 ; Rep. of the Sewage Commission. 



39 



