INTRODUCTION 5 



boiled sufficiently long, and be then sealed up so as to 

 prevent the access of air, they do not undergo putrefac- 

 tion ; (2) the sealing up may be dispensed with, provided 

 the air be first filtered through cotton-wool before being 

 admitted to the flasks ; and (3) even the cotton- wool 

 is not needed if the air be passed slowly through a long 

 and tortuous channel, so as to deposit its solid particles. 

 Tyndall showed that putrescible fluids may be exposed in 

 open vessels in a closed chamber the air of which has been 

 undisturbed for some time and its solid particles thereby 

 deposited on the walls of the chamber, which had been 

 smeared with glycerin ; he also proved that vegetable 

 infusions and the like, which putrefy after haying been 

 boiled for ten minutes, do not do so if the boiling be 

 repeated on two or three successive days, and explained 

 this by the supposition that while the fully developed 

 bacteria are destroyed by the first boiling, their more 

 resistant spores remain alive, but these on being left for 

 twenty-four hours germinate into the less resistant bacterial 

 forms, which are destroyed by the second boiling, and 

 by the repetition of the process complete sterilisation may 

 ultimately be obtained. This process of " discontinuous 

 sterilisation,'' as it is termed, is employed by the bacteri- 

 ologist to-day for the preparation ot sterile culture media. 1 

 The occurrence of abiogenesis (or as he preferred to 

 term it, " archebiosis ") was maintained by Bastian up 

 to his death in 1915. He claimed that certain saline 

 solutions which had been boiled, or even heated above 

 the boiling-point in sealed tubes, after a time show the 

 development of various living organisms, including 

 bacteria and yeasts. 2 



1 The writer believes that this explanation is only partially true, and 

 would ascribe some of the sterilising effect of repeated heatings simply to 

 the injurious action of alternate heating and cooling. 



2 See various papers in the Proc. Roy. Soc. Lond. The Evolution of Life, 

 Methuen, 1907 ; and Proc. Roy. Soc. Med. 1913. 



