BACTERIOLOGICAL STUDY OF WATER 



623 



Three of the sectors are subdivided into smaller areas of 

 equal size for convenience in counting when the colonies 

 are very numerous. The principles involved are similar 

 to those of the preceding apparatus, but the circular form 

 of the apparatus admits of more exactness when counting 

 colonies on a circular plate. ^ 



Fig. 109 



16 A 1 



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



Pakes^ has introduced a cheap and .convenient modifi- 

 cation of Lafar's apparatus. It consists of a sheet of white 

 paper on which is printed a black disk ruled with white 

 lines, in somewhat the same fashion as is Lafar's counter, 



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

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



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



