90 OUTLINES OF BACTERIOLOGY 



the temperature of boiling water is 1 00 C. If, now, the pressure is 

 in some way raised water will not boil until a higher temperature 

 is attained. In the autoclave increased pressure is obtained by pre- 

 venting the escape of steam. Otherwise it is the same in principle as 

 the Koch's steriliser. The apparatus must naturally be made very 

 strong, and the lid is made of some thick metallic substance with a 

 special appliance for keeping it down when the pressure rises. The 

 apparatus is shown in Fig. 67. For the practical working of this 

 apparatus the reader is referred to Arthur Meyer's Pmcticum der 

 botanischen Bakterienkunde. The sterilisation is most effective, as 

 even the most resistant of spores, e.g. those of Bac. subtilis, are 

 killed after about 20 minutes of 120C. of moist heat. The auto- 

 clave dispenses with the necessity of heating the object on three 

 successive days. 



The effect of the autoclave on the most resistant of spores is shown 

 in the following table : 



At 105-110C. 5 - killed in 2-4 hours. 

 ,. ll.VC., - 30-60 minutes. 



120 C., - 5-15 



125-130C., - 5 



140 C., - 1 



In one experiment it was found that the extremely resistant spores 

 of the potato bacillus succumbed in the following times : 



At 100 C., - after 5i-6 hours. 



i AQ 1 1 Q n I undecided, some still alive 



. . lUt/ 1 I O O., - - \ 11. 



} after f hour. 



,, 113-116C., - - after 25 minutes. 



122-123C., - 10 



126 C, - 3 



., 127 C., - - 2 



., 130C., - instantaneously. 



These results suffice to show the efficiency of this apparatus. 



If we turn now to light as a means of sterilisation we find that 

 whilst it has been proved that continual exposure to light is fatal 

 to bacteria, yet as a practical disinfectant it cannot be used owing 

 to the long time required before the bacteria can be killed. In the 

 case of spores it is doubtful whether their capacity for germination 

 is at all affected. The spores of soil-bacteria, for instance, must be 

 exposed for very long periods to the influence of sunlight. 



