56 BACTERIOLOGY 



or pieces of glass which have been sterilised. The same 

 process is gone through with the second and third inocula- 

 tions, and the three plates can be laid on benches one above 

 the other in a single moist chamber, or a separate one 

 appropriated to each of them. 



The moist chamber consists of a large glass box, which 

 is disinfected with corrosive sublimate solution and has a 

 circular piece of blotting-paper moistened with a 1 per 1,000 

 solution of the same substance laid upon the bottom (fig. 25). 



The plates prepared as above are left at the temperature 

 of an ordinary room until the individual cultures show them- 

 selves on the surface. These appear in the form of islets 



Gelatine plate 



Glass bench 

 FIG. 25. MOIST CIIAMBEE. 



either lying close together or isolated. Sometimes several 

 run into one another, and at times a dotted mass appears 

 on the plate, not unusually in the form of little clouds, all 

 of which vary in figure according to the kind of micro- 

 organism. Under a moderately high power of the microscope 

 the colonies are seen to be sharply defined, and sometimes 

 granular, sometimes fibrous, according to the manner in 

 which the micro-organisms are arranged in relation to one 

 another. If the microbes under observation are pigmented, 

 the individual colonies will appear of various tints, or the 

 colour may be diffused through the gelatine, and phosphores- 

 cence or fluorescence may be seen in single spots. By 

 comparison of all these peculiarities it is possible to isolate 



