210 AIDS TO BACTERIOLOGY 



by the Local Government Board (September, 1911) is 

 given as representing the considered opinion of the best 

 authorities on the subject: ' Ordinarily little is to be gained 

 by so doing. It is by no means certain that " ptomaines " 

 in the sense of alkaloidal substances produced by bacterial 

 action are present in meat foods which have caused 

 poisoning, and the significance of the reactions which are 

 held to demonstrate the presence of these substances is 

 a matter of considerable doubt.' 



The Bacteriology of Soil. 



Surface soil is very rich in bacteria, the number below 

 a depth of 1 metre being small. Frankel found that the 

 superficial layers of the soil of a fruit orchard contained 

 from 50,000 to 350,000 organisms per gramme. The 

 greatest number was at | to metre below the surface. 

 At a depth of from f to 1| metres there was a very abrupt 

 diminution in the number of bacteria. From 200,000 

 organisms at a depth of metre, the number fell to 2,000 

 at a depth of 1 metre, from 250,000 at f metre to 200 

 at 1 metre. In virgin soil there is a dividing-line at a 

 depth of from f metre to 1| metres, below which very 

 few bacteria are found, thus showing the ground water 

 region is quite free, or nearly free, from micro-organisms, 

 notwithstanding the vast number upon the surface of the 

 soil. 



Houston found surface virgin sandy soil to contain less 

 than 100,000 bacteria per gramme, other virgin soils 

 about 1,000,000, garden soil from 1,000,000 to 2,000,000, 

 and grossly-polluted surface soils up to 115,000,000 

 bacteria per gramme. Houston regards B. mycoides and 

 the Bismarck brown cladothrix as especially characteristic 

 of soil. 



James Buchanan Young found the soil of graveyards 

 to be very rich in micro-organisms, particularly those of 

 a liquefying type, Proteus vulgaris being present in 

 great numbers. Their action is so effective that he found 

 no notable quantities of organic carbon and nitrogen in 

 the upper layers, and not so very much more in the lower 

 layers than are found in virgin soil. He found, on the 

 whole, that the bodies do not greatly influence the number 

 of micro-organisms found. 



Two peat organisms, * O ' and ' Q' (Houston), produce 



