84 THE FLOATING-MATTER OF THE AIR. 



source of the crops which spring from our infusions 

 when impregnated by the floating particles of the at- 

 mosphere. 



§ 17. Recent Experiments on Heterogenesis. 



The uniform sterility of the boiled infusions described 

 in the foregoing pages, when protected from the floating 

 matter of the air, proves that they do not contain germs 

 capable of generating life. Our most advanced hetero- 

 genist, indeed, affirms that a temperatm-e of 140° Fahr. 

 reduces, in all cases, such germs to a state of actual or 

 potential death ; and he ingeniously argues that as, 

 even in flasks which have been raised to a temperature 

 of 212°, and hermetically sealed, putrefaction, and its 

 associated Bacteria, do most certainly arise, such Bac- 

 teria must be spontaneously generated. 'We know,* 

 he says, ' that boiled turnip or hay-infusions, exposed ta 

 ordinary air, exposed to filtered air, to calcined air, or 

 shut off altogether from contact with air, are more or 

 less prone to swarm with Bacteria and Vibriones in the 

 course of from two to six days.' ^ 



We are here met by a difficulty at the outset. The 

 proof of Bacterial death at 140° Fahr. consists solely in 

 the observed fact, that when a certain liquid is heated 

 to that temperature no life appears in it afterwards ; 

 while in another liquid life appears two days after it 

 has been heated to 212°. Instead of concluding that in 

 the one liquid life is destroyed and in the other not, it 

 is assumed that 140° Fahr. is the death-temperature for 

 both ; and this being so, the life observed in the second 

 liquid is regarded as a case of spontaneous generation. 

 A great deal of Dr. Bastian's most cogent reasoning 

 rests upon this foundation. Assumptions of this kind 

 guide him in his most serious experiments. He finds, 

 • 'Evolution and the Origin of Life,' p. 94. 



