598 THE POPULAR SCIENCE MONTHLY. 



any one of a hundred other putrid liquids, animal or vegetable. So 

 long as the liquid contains the living bacteria, a speck of it communi- 

 cated to the clear mineral solution, or to the clear turnip-infusion, 

 produces in twenty-four hours the effect that we have described. 



We now vary the experiment thus: Opening the back-door of an- 

 other closed chamber which has contained for months the pure mineral 

 solution and the pure turnip-infusion side by side, I drop into each of 

 them a small pinch of laboratory dust. The effect here is tardier than 

 when the speck of putrid liquid was employed. In three days, how- 

 ever, after its infection with the dust, the turnip-infusion is muddy, 

 and swarming as before with bacteria. But what about the mineral 

 solution which, in our first experiment, behaved in a manner undistin- 

 guishable from the turnip-juice ? At the end of three days there is 

 not a bacterium to be found in it. At the end of three weeks it is 

 equally innocent of bacterial life. We may repeat the experiment 

 with the solution and the infusion a hundred times, with the same 

 invariable result. Always in the case of the latter the sowing of the 

 atmospheric dust yields a crop of bacteria never in the former does 

 the dry germinal matter kindle into active life. 1 What is the infer- 

 ence which the reflecting mind must draw from this experiment ? Is 

 it not as clear as day that while both liquids are able to feed the 

 bacteria and to enable them to increase and multiply, after they have 

 been once fully developed, only one of the liquids is able to develop 

 into active bacteria the germinal dust of the air ? 



I invite my friend to reflect upon this conclusion ; he will, I think, 

 see that there is no escape from it. He may, if he prefers it, hold the 

 opinion, which I consider erroneous, that bacteria exist in the air, not 

 as germs but as desiccated organisms. The inference remains that, 

 while the one liquid is able to force the passage from the inactive to 

 the active state, the other is not. 



But this is not at all the inference which has been drawn from 

 experiments with the mineral solution. Seeing its ability to nourish 

 bacteria when once inoculated with the living active organism, and 

 observing that no bacteria appeared in the solution after lofig ex- 

 posure to the air, the inference was drawn that neither bacteria nor 

 their germs existed in the air. Throughout Germany the ablest lit- 

 erature of the subject, even that opposed to heterogeny, is infected 

 with this error; while heterogenists at home and abroad have based 

 upon it a triumphant demonstration of their doctrine. It is proved, 

 they say, by the deportment of the mineral solution that neither 

 bacteria nor their germs exist in the air ; hence, if, on exposing a 

 thoroughly sterilized turnip-infusion to the air, bacteria appear, they 

 must of necessity have been spontaneously generated. In the words 



1 This is the deportment of the mineral solution as described by others. My own 

 experiments would lead me to say that the development of the bacteria, though exceed- 

 ingly slow and difficult, is not impossible. 



