1 76 LEISURE-TIME STUDIES. 



this rule. We have thus at the outset many circumstances- 

 presented to us, favouring the a priori consideration that 

 we are dealing with conditions affecting rather the ordinary 

 life and development of lower organisms, than the develop- 

 ment of such beings in some mysterious and inexplicable 

 fashion from non-living materials. Continental experi- 

 menters and investigators at home are perfectly agreed that 

 organisms will appear in fluids treated and protected as 

 already described; and some valuable additional informa- 

 tion has been contributed regarding the effects which the 

 specific or chemical nature of the solutions appears to pro- 

 duce on the development of life within them. Thus it has 

 been ascertained that when infusions of hay always a 

 favourite substance with experimenters are rendered acid, 

 they exhibit a development of organisms less readily than 

 when rendered alkaline or neutral. 



The test-points to which experiments on spontaneous 

 generation have led in the present day, appear to resolve 

 themselves into a first query regarding the degree of heat 

 capable of completely destroying not only the adult organ- 

 isms which appear in infusions, but their germs also ; and a 

 second respecting the nature of the conditions within or 

 without the infusions which may retard or favour the vitality 

 of these lower organisms. An ingenious mode of deter- 

 mining the degree of heat necessary to kill the bacteria and 

 other organisms found in fluids was devised by Dr. Bastian. 

 A solution of some chemical salt, for example, is found, 

 when protected from external influences, to show no dispo- 

 sition to generate living beings. But if such a solution be 

 infected with a drop of fluid containing organisms, the latter 

 will generate and multiply in the chemical solution as readily 

 as within an ordinary infusion. By pursuing such a mode 

 of experimentation, Dr. Bastian found that he could assure 

 himself of the presence of bacteria in a pure fluid by 

 actually conveying them into it, and that, having obtained 

 these conditions to begin with, he could in the next instance 

 experiment with some hope of arriving at a definite result 



