THE SCOPE OF BIOLOGY 



13 



show a world of invisible life, and in the various bottles and 

 flasks used in these early experiments, a large number of micro- 

 scopic forms of life appeared in spite of all attempts made to 

 prevent their entrance. Although in a piece of meat no fly 

 maggots developed unless flies had previous access to the meat, 

 innumerable microscopic forms of life did appear in it, in spite 

 of all efforts to exclude them, even when the meat was care- 

 fully and hermetically sealed. Some of the early experimenters 

 naturally concluded that these microscopic forms of life ap- 

 peared spontaneously, while others insisted that these little 

 organisms had found entrance into the sealed vessels from the 

 outside, in spite of all precautions taken to keep them out. 

 Great ingenuity was shown in devising experiments for settling 

 this question. The results obtained by different experimenters 

 were in great conflict for over two centuries, and apparently 

 equally good evidence 

 was found both for and 

 against the belief in 

 spontaneous genera- 

 tion. 



Needham and Spal- 

 lanzani. The general 

 method used by the 

 experimenters was to 

 place meat, hay infu- 

 sions, cheese, etc., in 

 flasks, and then by 

 boiling to attempt to 

 kill all life in the ma- 

 terial, and later, by 

 sealing hermetically, 

 to guard against the entrance of any form of microscopic life from 

 without. But even under these conditions it was frequently found 

 that microscopic life made its appearance in the sealed vessels ; 

 Fig. 2. It proved very difficult to be sure that nothing was left 



FIG. 2. APPARATUS USED BY SCHWANN IN 

 EXPERIMENTING ON SPONTANEOUS GENERA- 

 TION 



Steam produced by boiling passed out through the 

 tube, but upon cooling was drawn in again through the 

 heated coil, which sterilized it. 



