QUANTITATIVE BACTERIOLOGICAL ANALYSIS. 23 



relation between the number of organisms and the chemical 

 composition of the water. 



Bolton's work pointed in the same direction ; he distinctly 

 said that the chemical composition of a water had no relation to 

 the number of micro-organisms. 



Tiemann and Gartner believe that, in relation to nutritive 

 material, bacteria may be arranged in two groups. The first 

 group includes the water bacteria, which have very slight 

 dependence on the nutritive material present, and under favour- 

 able conditions multiply rapidly. The second group embraces 

 those organisms which are greatly dependent on the nutritive 

 material present, and are derived from the earth and living 

 beings. 



With regard to the organic matter the difficulties are 

 very great ; we are not able to determine exactly which of the 

 constituents form suitable food for bacteria, indeed Duclaux 

 has said that the quality of the organic matter is far more 

 important than the quantity. Using the oxygen derived from 

 potassium permanganate as a test, Fischer found in one case 7*4 

 parts per 100,000 of oxygen absorbed with 800 bacteria present, 

 and in another case only 0*5 part per 100,000 of oxygen 

 absorbed with 360,000 bacteria present. Tiemann and Gartner 

 investigated the effect of inorganic substances, especially lime 

 salts and total solids on the bacterial contents ; the results 

 obtained were as follows : 



Total soliJs. Organisms per c.c. 



0-50 81 



50-100 261 



100-150 250 



200-500 46 



These results show that often a high bacterial count is 

 associated with high total solids, but with an excess of solids the 

 organisms may diminish again. 



A review of all the experiments appears to justify the 



