350 THE BEGINNINGS OF LIFE. 



cessive pressure certainly does occur, and occasionally it 

 has been so extreme as to cause a rupture of the vessel 1 . 

 The tension within the flask was thought likely to be 

 especially unfavourable to the occurrence of fermen- 

 tation or putrefaction, since it had been experimentally 

 proved by Mr. Sorby 2 that pressure does undoubtedly 

 influence c chemical changes taking place slowly/ and 

 which are therefore c probably due to weak or nearly 

 counterbalanced affinities/ This influence of pressure 

 in checking chemical change is more especially seen in 

 cases where the chemical actions are accompanied by 

 the evolution of a gas. So that, as Mr. Sorby adds, c it 

 may cause a compound to be permanent, which would 

 otherwise be decomposed.' For these reasons I was led 

 to adopt the following method of experimentation : 

 After each flask had been thoroughly cleaned with 



had boiled an infusion of hay for four hours, and had then hermetically 

 sealed the neck of the flask whilst ebullition continued. In this way a 

 more or less perfect vacuum was procured. This he did as a sort of 

 tentative experiment ; but it was then, on thinking over the subject, that 

 I resolved to give the plan a thorough trial, as it appeared to me that 

 by so doing I should be working under conditions which were most in 

 accordance with the theory of evolution. I performed four experiments 

 at that time in concert with Mr. Temple Orme, with hay infusions, 

 which had been boiled for four hours, and had then been sealed up in 

 vacua. In each of these fluids, organisms were found after a com- 

 paratively short time. These were the first experiments performed 

 under such conditions. In my subsequent work I have not had the 

 benefit of Mr. Orme's personal assistance, although I. have frequently 

 profited by suggestions which he has made. 



1 ' Essays on Physiological Subjects,' and ed., 1869, pp. 113, 114. 



2 Bakerian Lecture 'On the Direct Correlation of Mechanical and 

 Chemical Forces.' (Proceed, of Royal Society, 1863, pp. 546 and 539.) 



