26 



forms also a large round head on the surface, so that it looks 

 very like a tenpenny nail ; the third, the m. osteomyelitis, 

 found in certain diseases of bones, liquifies the gelatine, 

 forming a white film on its surface, and a red sediment at 

 the bottom ; whilst the fourth grows in a yellow mass on the 

 surface. 



Quite different from any of these, the Bacillus of 

 Anthrax, grows out in a thick cloud from the needle track, 

 and ultimately liquifies the gelatine ; whilst that which 

 produces septicaemia, or blood poisoning, in mice, grows in a 

 very delicate thin cloud, and does not liquify the gelatine. 



If it be desired to separate Bacteria from one another, 

 or from tissues in which they are growing, plate cultivations 

 are made use of. A test tube is inoculated in the ordinary 

 way; but as this will contain too great a number of organisms, 

 the jelly is melted by immersing the tube in warm water at 

 40°C., shaken up, and a little of it poured iato another tube. 

 The jelly in this is again melted and shaken up, and poured 

 out carefully on to a piece of sterilised, plate glass, about two 

 inches square. This is placed on moist blotting paper, on an 

 ordinary plate, and covered over with a bell glass. The 

 micro-organisms will be separated by this process, and a 

 colony will grow round each one. As nearly every Bacterium 

 produces a different shaped colony, any one may be picked 

 out, on the point of a platinum needle, under an inch or half 

 inch lens, and a test tube may be inoculated with it ; thus, 

 what are called ^' pure cultivations" are made. 



To examine micro-organisms whilst growing, especially 

 to see the formation of spores, a small quantity of the jelly 

 may be placed in a glass cell, with a cover glass over it, 

 luted with vaseline, and inoculated in the usual way. 



Micro-organisms grow best at different temperatures, 



according to the species, and an incubator is necessary for 



'^ose which require summer heat or more. This is a tin 



ox, with double walls containing water, which is kept warm 



by a Bunsen's burner beneath it. The heat may be regulated 



by a Page's regulator ; and the one in the room has some- 



