338 APPENDIX. 



this period the germs are being prepared for their emer- 

 gence into the finished organism. They reach the end of 

 this period of preparation successively — 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 pre- 

 paration of the infusion), I subject it for a brief interval 

 to a temperature which may be under that of boiling 

 water. Such softened and. vivified germs as are on the 

 point of passing into active life are thereby killed ; others 

 not yet softened remain intact. I repeat this process well 

 within the interval necessary for the most advanced of 

 those others to finish their period of latency. The number 

 of undestroyed germs is further diminished by tbis second 

 heating. After a number of repetitions, which varies with 

 the character of the germs, the infusion, however obstinate, 

 is completely sterilized. 



The periods of heating need not exceed a fraction of 

 a minute in duration. Sum them up in the case of an 

 infusion which they have perfectly sterilized ; they amount 

 altogether to, say, five minutes. Boil another sample of 

 the same infusion continuously for fifteen or even sixty 

 minutes, you fail to sterilize it, although the temperature 

 is higher and its time of application more than tenfold 

 that which, discontinuously applied, infallibly produces 

 barrenness. 



In a few weeks I hope to bring this entire subject 

 under the notice of the E/oyal Society ; meanwhile, if you 

 think it would interest them, I should be glad if you 

 would communicate to the Fellows this general statement 

 of the most recent results of experiment. 



Believe me, 



Ever faithfully yours, 



John Tyndall. 

 T. E. Huxleij, Esq., Sec. RS. 



Spottistcoode d: Co., Printers, New-street Square, London. 



