292 BIOLOGY AND ITS MAKERS 



ble matter. It is to be noted that the test tubes were n< 

 corked and consequently that the fluids contained within 

 them were freely exposed to the optically pure air- within the 

 chamber. 



The box was now lifted, and the ends of the tubes extend- 

 ing below it were thrust into a bath of boiling oil. This set 

 the fluids into a state of boiling, the purpose being to kill 

 any germs of life that might be accidentally introduced into 

 them in the course of their conveyance to the test tubes. 

 These fluids, exposed freely to the optically pure air within 

 this chamber, then remained indefinitely free from micro- 

 organisms, thus demonstrating that putrescible fluids may 

 be freely exposed to air from which the floating particles 

 have been removed, and not show a trace either of spoiling 

 or of organic life within them. 



It might be objected that the continued boiling of the 

 fluids had produced chemical changes inimical to life, or in 

 some way destroyed their life-supporting properties; but 

 after they had remained for months in a perfectly clear state, 

 Tyndall opened the little door in the back of the box and 

 closed it at once, thereby admitting some of the floating 

 particles from the outside air. Within a few days' time the 

 fluids which previously had remained uncontaminated were 

 spoiling and teeming with living organisms. 



These experiments showed that under the conditions of 

 the experiments no spontaneous origin of life takes place. 

 But while we must regard the hypothesis of spontaneous 

 generation as thus having been disproved on an experimental 

 basis, it is still adhered to from the theoretical standpoint 

 by many naturalists; and there are also many who think 

 that life arises spontaneously at the present time in ultra- 

 microscopic particles. Weismann's hypothetical " biophors," 

 too minute for microscopic observation, are supposed to arise 

 by spontaneous generation. This phase of the question, 



