SPONTANEOUS GENERATION 299 



ably energetic way." Thus he considered these living 

 objects to be animals, from their motion, and this belief 

 held sway for nearly two hundred years. 



Leeuwenhoek was a pure observer of facts and made no 

 attempt at speculation, but his discoveries soon started the 

 theorists to discussing the origin of these minute organisms. 

 Most observers, as was probably to be expected, believed 

 that they arose spontaneously. Needham, in 1749, described 

 the development of microorganisms around grains of barley 

 in water. Bonnet, in 1768, suggested that probably Need- 

 ham's animalcules came from ova in the liquid. The Abbot 



B& 



Zt ^^- 



Fig. 170.— The first drawings of bacteria by Leeuwenhoek. The dotted line 

 C to D indicates the movement of the organism. 



Spallanzani, in 1769, called attention to the crudeness of 

 Needham's methods and later, in 1776, attempted to dis- 

 prove spontaneous origin by heating infusions of organic 

 material in flasks and then sealing them. His critics raised 

 the objections that heating the liquids destroyed their 

 ability to support life, and that sealing prevented the access 

 of fresh, air which was also necessary. The first objection 

 was disproved by the accidental cracking of some of the 

 flasks which thereafter showed an abundant growth. This 

 accident seemed also to support the second objection, and 

 Spallanzani did not answer it. Though Spallanzani's experi- 

 ments failed to convince his opponents, they led to important 



