110 BACTERIOLOGY. 



the same remark applies equally to all preparations tube- cultures, 

 potato-cultures, drop-cultures, etc. 



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, the time 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 the 

 colonies will also be very numerous, but retain their isolated position 

 for a longer time ; while on the uppermost plate the colonies are 

 completely isolated from one another, with an appreciable surface of 

 gelatine intervening. 



Examination of Plate- cultivations. The macroscopical appear- 

 ances of the colonies are best studied by placing the plate on a 



FIG. 39. DAMP CHAMBER CONTAINING PLATE-CULTIVATIONS. 



slab of blackened glass, or on a porcelain slab if the colonies are 

 coloured. 



To examine the microscopical appearances, a selected plate is 

 placed upon the stage of the microscope. The smallest diaphragm 

 is employed, and the appearances studied principally with a low 

 power. These appearances should be carefully noted, and a 

 sketch or photograph of the colony made. The morphological 

 characteristics of the micro-organisms of which the colony is formed 

 can be examined in the following way : A small looped or 

 hooked platinum needle is held like a pen. and the hand steadied 

 by resting the little finger on the stage of the microscope. The 

 extremity of the needle is steadily directed to the space between 

 the lens and the gelatine without touching the latter, until, 011 

 looking through the microscope, it can be seen in the field, above 

 or by the side of the colony under examination. The needle 

 is then dipped into the colony, steadily raised, and withdrawn. 

 Without removing the eye from the microscope this manipulation 

 can be seen to be successful by the colony being disorganised or 



