BACTERIOLOGICAL STUDY OF WATER. 637 



preceding apparatus, but the circular form of the appa- 

 ratus admits of more exactness when counting colonies 

 on a circular plate. 1 



Pakes 2 has introduced a cheap and convenient modi- 

 fication of Lafar's apparatus. It consists of a sheet of 

 white paper on which is printed a black disk ruled 



- 



8 



Pakes's apparatus for counting colonies (reduced one-third). 



with white lines, in somewhat the same fashion as is 

 Lafar's counter, though the areas of the smallest sub- 

 divisions are not of one size and do not bear a constant 



1 Lafar's apparatus is to be obtained from F. Mollenkopf, 10 Thor- 

 strasse, Stuttgart, who holds the patent for it. Its price is about 8 

 marks. 



2 Journal of Bacteriology and Pathology, 1896, vol. iv. No. 1. 



