58 



SOLID CULTIVATION MEDIA. 



respectively, if the potatoes are of very large or small size) in this 

 position, and the water must be kept boiling the whole of that time. 





Fig. 15. — Bacillus anthracis growing on sterilised potato. The 

 growth has a succulent appearance, and forms an elevated plateau 

 with rounded edges. 



The potato-holder is now removed, and is placed on a layer of filter 

 paper, soaked with a one per cent, solution of perchloride of mercury, 

 to prevent contamination from the ingress of germs from below 

 carried by currents of heated air, whilst the lid is very slightly raised 

 at one side to allow the steam to escape, and at the same time to 

 prevent access of germs from above. 



Whilst they are thus cooling, preparations must be made for 

 receiving the potatoes into sterile chambers. Shallow glass bells (Fig. 

 17) are prepared for their reception, by thoroughly rinsing them 

 with the corrosive sublimate solution (HgCL 1%). The lower half 

 of each bell is provided with a double layer of filter paper, which 

 accurately fits its floor, and this is also soaked with the same solution. 

 The bell thus prepared is allowed to stand an hour or two before 

 use, to permit of subsidence of dust and spores in the contained air, 

 and is kept carefully closed till the moment when the sterile potatoes 

 are introduced. 



