PURE CULTURES OF 



number of flasks containing nutrient liquid, each with or\e drop 

 of this mixture, it was found that some remained sterile, 

 and Lister then assumed that each of the remaining flasks 

 contained a pure culture. The counting was carried out in 

 ordinary microscopic preparations. The same method was 

 subsequently employed by Nageli and by Fitz. There is, 

 however, no certainty about this method, and it is found that, 

 in spite of the calculation, several of the inoculated flasks 

 received more than one germ each ; but since an absolute 

 guarantee is only attained with a single cell culture, the 

 problem which I set myself was to carry out this principle. 

 In the case of yeast cells, I succeeded in my object towards 

 the end of 1881. (My first publication in connection with 

 this appeared in February 1882, in the ' Compte rendu du 

 Laboratoire de Carlsberg,' Copenhagen, I vol., 4 livr. p. 212. 

 A detailed description of my methods is given in the same 

 journal, 2 vol. 2 livr.) 



The method of counting which I adopted differed from 

 that employed by Lister, in that I made use partly of the 

 haemati meter, and partly of a special cover-glass divided into 

 squares for the purpose (Fig. i). One drop of the liquid 

 containing the yeast cells is placed on the cover-glass, and 

 within the limits of the large square, the small squares having 



FIG. i. FIG. 2. 



merely the object of assisting in the counting. The cover- 

 glass with the drop on its under surface is fixed to the ring 

 of the moist chamber (Fig. 2). If we now find that the drop 

 contains, e. g. 20 cells, and we then introduce it into 40 cc. of 

 sterilised water, we shall have assuming that we are work- 

 ing with average samples only one cell in every two cubic 



