INTRODUCTION 5 



faction ; (2) that the sealing up may be dispensed with, 

 provided the air be first filtered through cotton-wool before 

 being admitted to the flasks ; (3) that 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 in which the 

 air 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 

 having 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 com- 

 plete sterilisation may ultimately be obtained. It is 

 this process of " discontinuous sterilisation," as it is 

 termed, which is employed by the bacteriologist for the 

 preparation of sterile culture media. 1 



The occurrence of abiogenesis (or as he prefers to term 

 it, " archebiosis ") is still maintained by Bastian. He 

 claims that certain saline solutions which have 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 



Dunbar, 3 as the result of a series of experiments con- 



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. 



3 See Journ. Roy. Inst. Pub. Health, vol. xv, No. 11, 1907, p. 679. 



