1877.] 



Prof. J. Tyndall on Heat as a Germicide. 



569 



gations of this kind, to be acquainted with some o£ the causes of failure 

 which I have met with, and to know how small the difference of the 

 variations probably is when we ascend to a considerable height in the 

 atmosphere. The results I have obtained from two instruments placed 

 in positions so greatly different as those of the cloudy mountain-peak and 

 the sunny plain, will also show the degree of accuracy attainable when 

 the requisite precautions are taken, and accurate methods of correction 

 and reduction have been employed. 



VI. " On Heat as a Germicide when Discontinuoiisly Applied.^'' 

 By John Tyndall, F.R.S, Received February 14, 1877. 



Eoyal lustltutiou, Feb. 14tli, 1877. 



My deae Huxley, — In my " Preliminary Note," communicated to the 

 Eoyal 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 soui'ce ; aud 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 interest you to learn that the most obstinate of 

 the infusions referred to in the " Note " have been since rendered tract- 

 able by the application of very simple means. Following up the plain 

 suggestions of the germ theory, I have been able, e^'en in the midst of a 

 virulently infective atmosphere, to sterilize all the infusions by a tempera- 

 ture 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 appKed. 

 For example, I boil an infusion for fifteen minutes, expose it to a tem- 

 perature of 90° Fahr., and find it twenty-four hours afterwards swarming 

 with life. I submit a second sample of the same infusion to a tempera- 

 ture lower than that of boiling water for five minutes, and it is rendered 

 ]}ermanently 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. During this period the germs are being prepared for their 

 emergence into the finished organism. They reach the end of this period 

 of preparation successive^ — the period of latency of any germ depending 

 upon its condition as regards dryness and induration. This, then, is my 

 mode of proceeding: — Before the latent period of any of the germs 

 has been completed (say a few hours after the preparation of the infu- 

 sion), I subject it for a brief interval to a temperature which Diay be 



