APPENBIX. 337 



The method of ' Discontinuous Heating ' was first described 

 in the following letter to Professor Huxley.^ 



Royal Institution, Feb. 14, 1877. 

 Mt deae Huxlet, — In my ' Preliminary Note,' communi- 

 cated to the Boyal Society on the 18th of January, various 

 infusions were referred to as manifesting an astonishing 

 resistance to sterilization by heat. This resistance was 

 traced to its source ; and I have been since informed that 

 you were good enough to express at the time a very 

 favourable opinion as to the significance and value of the 

 results indicated. 



It will, I think, now iaterest you to learn that the most 

 obstinate of the infusions referred to in the ' Note ' have 

 been since rendered tractable by the application of very 

 simple means. Following up the plain suggestions of 

 the germ theory, I have been able, even in the midst 

 of a virulently infective atmosphere, to sterilize all the 

 infusions by a temperature lower than that of boiling 

 water. 



It is known that the prolonged application of a low 

 temperature is often equivalent to the brief application of 

 a higher one ; and you may therefore be disposed to 

 conclude that in the experiments here referred to I have 

 substituted time for intensity. This, however, is not the 

 case. The result depends solely upon the manner in 

 which the heat is applied. For example, I boil an infusion 

 for fifteen minutes, expose it to a temperature of 90° 

 Fahr., and find it twenty-four hours afterwards swarm- 

 ing with life. I submit a second sample of the same 

 infusion to a temperature lower than that of boiling 

 water for five minutes, and it is rendered permanently 

 barren. 



The secret of success here is an open one. I have 

 already referred to the period of latency which precedes 

 the clouding of infusions with visible Bacteria. Daring 

 ' From the Proceedings of the Eoyal Society, No. 178, 1877. 



