REPRODUCTION 



Wi 



in 1861 devised a flask (Fig. 125) with a tube fused in the side. The 

 tube was so bent (down, then up, then down) that no particle of dust 

 could pass the curve in which a droplet of water was left by condensation 

 after l)oiling. When the flask had been partly filled with putrcscible 

 material and then sterilized its contents remained without putrefaction. 

 Pasteur's experiments were so carefully carried on and were so extensive 

 that the idea of spontaneous generation in its old form was generally 

 abandoned. Careful experiments by the physicist Tyndall and the 

 work of Lord Lister who made application of the results of Pasteur to 

 surgery did much by confirming Pasteur's teachings to overthrow the 



idea of spontaneous generation. 



Pasteur's investigations and teach- 

 ing resuItedTiETthe origin of a whole 

 new field of biological investigation, 

 T namely, bacteriology.. The investiga- 

  tions of the bacteriologists show 

 beyond a doubt that bacteria are not 

 ":• now originating de novo in cultures. 

 Bacteria originate only from preexist- 



FiG. 124. Fig. 125. 



Fig. 124. — Louis Pasteur, 1822-1895. (From Garrison's History of Medicine, W. B. 

 Saunders Co.) 



Fig. 125. — Flask used by Pasteur in experiments upon spontaneous generation. The 

 open top was sealed aftei the flask was filled with a nutrient solution. After boiling, water 

 vapor condensed and filled the low curve in the side tube thus preventing access of organ- 

 isms borne by the air. {After MacFailand.) 



ing bacteria. If a bacteriologist finds in a culture a bacterium which he 

 did not put there he ascribes its presence to contamination through air 

 currents or instruments, or to faulty sterilization. The old idea of spon- 

 taneous generation is now recognized as untenable, and present-day 

 organisms are known to arise only from previously existing organisms 

 through some form of reproduction. 



Modern Idea of Spontaneous Generation. — Many biologists believe 

 that while living things arc not originating under present conditions, life 

 at some time in the past originated ]\v a combination of the proper 

 elements when conditions were other than at present. This belief is 

 sometimes designated as the modern theory of spontaneous generation. 



