MIGRO-OEGANISMS IN WATER 



Thermometer 



■Lid 



"Water-gauge 



Eiug of flames 



freely from the top. In this way a uniform tempera- 

 ture of 100° C. is obtained, and for the sterilisation of 



glass and other vessels 

 an exposure of from one 

 to two hours is neces- 

 sary. In the case of 

 some culture materials, 

 however, such pro- 

 longed heating to so 

 high a temperature 

 would cause serious 

 alteration, and the prac- 

 tice of intermittent steri- 

 lisation (Tyndall) is then 

 resorted to. This me- 

 thod is also of impor- 

 ^IL* tance in the case of 

 those materials, such as 

 potatoes, in which one 

 exposure only to this temperature does not actually 

 ensure sterility. T^mdall's plan is to submit substances 

 to a high temperature for a short time on three to five 

 successive days, and in the preparation of culture media 

 containing gelatine this discontinuous sterilisation is 

 of primary importance, as prolonged steaming greatly 

 reduces the melting-point of the gelatine. Sterilisation 

 may also be effected by simply boiling the articles in 

 water ; thus in the disinfection of instruments — syringes 

 &c. — used in animal inoculations this may frequently 

 be resorted to with advantage. 



In some exceptional cases, e.g.^ in the sterilisation 

 of soil, high-pressure steam may be very conveniently 

 used; thus certain spores were found by Globig ('Zeitsch. 

 f. Hygiene,' iii. [1887], p. 332) to resist the ordinary 

 process of steaming for upwards of three hours, whilst 



JC^^ 



Fig. 1. — Koch's Steam Steriliser. 



