28 MICRO-ORGANISMS IN WATER 



Uschinskys l Solutions. For the study of the toxic 

 bodies produced, this author has successfully cultivated 

 pathogenic bacteria in the following solution free from 

 albumen : 



Water . . . 1,000 grams 1 Magnesium sulphate . '2 gram 



Glycerin . . 40-50 Dipotassium phosphate TO 



Sodium chloride . 5-7 Ammonium lactate . 10*0 grams 



Calcium chloride . -1 gram 



whilst in the following solution he found that they not 

 only grew luxuriantly, but in some cases even more so 

 than in broth : 



Water . . . 1,000 grams 

 Glycerin . . 30-40 

 Sodium chloride . 5-7 ,, 

 Calcium chloride . -1 gram 



Magnesium sulphate '2--4 



Dipotassium phos- 

 phate . . . 2-2'5 grams 

 Ammonium lactate . 6-7 

 Sodium aspartate . 3 "4 ,, 



METHODS FOR THE ISOLATION OF MICRO-ORGANISMS 



Dilution Method. This method consists in so largely 

 diluting the liquid containing the micro-organisms, and 

 then dividing this diluted material into such a number 

 of small fractions, that each of these fractions contains 

 not more than one micro-organism. Such a fraction 

 then forms the starting-point for a pure culture of the 

 particular organism. 



Although the principle underlying this method is 

 obvious enough, and is comprised in these few words, 

 yet its actual execution is in the highest degree laborious 

 and wearisome, success often only being achieved after 

 many abortive attempts. An idea of the manner in 

 which this method is carried out may be gathered from 

 the following hypothetical case : 



Suppose that it has been estimated, by microscopic 

 examination, that about 10,000 microbes are present in 

 one cubic centimetre (about 20 drops) of a given liquid: 



1 CeniralUatt fur Bakteriologie, vol. xiv. 1893, p. 316. 



