STERILISER 31 



apparatus which cannot be exposed to temperatures above 

 100 C. Glass utensils may be steamed for from one to 

 two hours. 



The High-Pressure Steam Steriliser. High-pressure 

 steam in an autoclave acts with greater rapidity than 

 ordinary steam. Although not necessary for ordinary 

 use, in the sterilisation of soil it must be used. Certain 

 spores resist ordinary steaming for three hours, but 

 are destroyed in fifteen minutes by steam at 110 to 

 120 C. 



Sterilisation by Chemical Agents. For washing instru- 

 ments, and for disinfecting the hands, solutions of 1 in 

 1,000 of corrosive sublimate, 1 in 20 solution of phenol, or 

 1 in 50 solution of lysol, are used. When chemical agents 

 are used, risk is incurred by traces of the germicide escaping 

 removal, and destroying the organisms under examination 

 or introducing other elements of uncertainty into the 

 work. For ordinary purposes it is best to rely upon the 

 careful fulfilment of all the details required in the sterilisa- 

 tion by the usual methods. 



Glass pipettes, etc., may be rapidly sterilised by rinsing 

 with o per cent, phenol, then with absolute alcohol, and 

 lastly with ether, the ether finally being driven off by 

 careful heating over the Bunsen. 



Steel instruments, etc., are best boiled in water con- 

 taining a little sodium carbonate. 



Sterilisation by Filtration. Air and other gases are 

 readily freed from micro-organisms by drawing them 

 through a tube containing a plug of dry sterile cotton- 

 wool or packed with sugar or sand. 



Water or other liquid which is not too viscid is sterilised 

 by passage through unglazed porcelain cylinders (Pasteur- 

 Chamberland filter). These filters are used for the pur- 

 poses of concentration of bacteria in a liquid, or the separa- 

 tion of bacteria from their products. 



For experimental purposes these filters must be cleaned 

 and sterilised before being used. This operation does 

 not affect the Pasteur filter, but tends to disintegrate the 

 Berkefeld (see p. 239). 



The Microtome. A large number of machines for the 

 cutting of sections of tissues have been introduced. For 

 some the tissue is frozen before cutting, for others it is 

 first impregnated with paraffin or celloidin. 



