292 A MANUAL OF BACTERIOLOGY 



with the aid of Wolffhugel's counting apparatus 

 (see Fig. 55), which consists of a glass plate, ruled 

 with vertical and horizontal lines into centimetre 

 squares, which are often sub-divided. The cultiva- 

 tion-plate is placed on a black background, and the 

 ruled glass plate placed over the former, without 

 touching the colonies. 'If the colonies are very 

 numerous the number in some small divisions is 

 counted ; if less, in some large ones ; and an average 

 is obtained from which the number of colonies on 

 the entire surface is calculated.' 



The second method is largely used in France, 

 and is known as ' fractionnement dans le bouillon.' 

 The sample is first diluted with sterilised water of 

 known volume. After this one gramme (1 cc.) of 

 the water is taken up by means of a sterilised capil- 

 lary pipette, which is dipped four times into the 

 water at different points of the liquid mass to 

 obtain the above-mentioned quantity. By this 

 means a fair sample of the water is obtained. In 

 the laboratory of Dr. P. Miquel thirty-six small 

 flasks (each 15 cc. capacity) are each half filled 

 with sterilised bouillon. These flasks, having each a 

 glass cap containing a sterilised cotton-wool plug, 

 are placed in a divided box. Each flask receives 

 one, two, or three drops of the sample of water, as 

 the case may be; all the flasks are placed in an 

 incubator at 30-36 C. during a period of at least 

 fifteen days, when the microbian colonies are 

 counted. 



Before introducing the small quantity of water 

 into either a solid or a liquid medium, the original 



