stevens] EXPERIMENT ON SPONTANEOUS GENERA TION 29 



there with a microscope. The germs which were planted in No. 4 

 began to grow and multiply rapidly, increasing from a few thousand to 

 many billions and causing putrefaction of the broth, with its accom- 

 panying bad odors as they did so. Tube No. 1 if left unopened 

 would remain sweet and clear for years, while any tube would imme- 

 diately begin to decay if dust were added. But how did the germs 

 get into tube No. 3 ? Let us see. This tube was left open thirty 

 minutes. Dust very similar to that put in No. 4 is floating about in 

 the air. It is quite possible that during the thirty minutes some such 

 particles may have fallen into the tube. If we find any indication of 

 germ life in Tube No. 3 it is quite certain that the germs gained 

 entrance from the air. With tube No. 2 the conditions are very sim- 

 ilar, except owing to the shortness of the exposure the probability of 

 decay is much less. 



To tubes Nos. 5 and 6 we are certain that we added germs with 

 the dust. Why did these tubes not putrefy? It is evident that the 

 boiling to which No. 5 was subjected, and the carbolic acid placed in 

 No. 6, either killed the germs or prevented their growth. The decay- 

 ing of No. 7 shows that even a drop of drinking water bears with it 

 germs. 



The experiment is quite convincing and forces us to the conclu- 

 sion that when substances are properly sterilized and all germs pre- 

 vented from entering no putrefaction will result and no germ life 

 appear. If, however, germs be added to these sterile putrescible 

 substances the germs will develop in immense numbers and the liquids 

 will consequently decay. In no case, if the work be carefully done, 

 will the germs appear in the sterile tubes unless they have gained 

 access from the outside. That they can come into existence spon- 

 taneously, without parentage, seems impossible after this experiment 

 has been made. Not only has such an experiment been made once 

 but many times with unfailing success, and many important industrial 

 and hygienic practices have been based upon the conclusions afforded 

 by it and lasting benefits of untold value to mankind have resulted. 



