PL ATE- CULTIVATIONS. 73 



Corresponding with the fractional cultivation of 

 the micro-organisms obtained in this manner, the 

 colonies will be found to develop in the course of a 

 day or two, varying with the temperature of the 

 room. The lower plate will contain a countless 

 number of colonies which, if the micro-organism 

 liquefies gelatine, speedily commingle, and produce, 

 in a very short time, a complete liquefaction of the 

 whole of the gelatine. On the middle plate, with 

 the first attenuation, the colonies will also be very 

 numerous, but retain their isolated position for a 

 longer time ; while on the uppermost plate, the 

 second attenuation, the colonies are completely 

 isolated from one another, with an appreciable 

 surface of gelatine intervening. 



Examination of Plate- cultivations. The 

 macroscopical appearances of the colonies are best 

 studied by placing the plate on the slab of blackened 

 glass, or on the porcelain slab if the colonies are 

 coloured. 



To examine the microscopical appearances a 

 selected plate is placed upon the stage of the 

 microscope ; it is better to have a larger stage than 

 usual for this purpose. The smallest diaphragm is 

 employed, and the appearances studied principally 

 with a low power. These appearances should be 

 carefully noted, and a rapid sketch of the colony 

 made. The morphological characteristics of the 

 micro-organisms of which the colony is formed can 

 then be examined in the following way. A small 



