82 Fermentation and Kindred Phenomena. 



was the Italian Redi, who, by a very simple experiment, proved 

 that flies are not produced spontaneously from putrefying meat. 

 He merely enclosed fresh meat in a gauze cage, and observed 

 that although the latter putrefied no maggots nor flies were 

 developed in it. He watched the flies hovering over the enclosed 

 meat, and by a mistaken instinct depositing their eggs in the 

 gauze cage, and eventually he saw these eggs turn into maggots. 

 He thus proved, by an experiment which we may agree with 

 Huxley in calling childishly simple, that insects are produced 

 from their parents and not spontaneously as a product of 

 corruption. Redi's experiments were sufficiently conclusive 

 with regard to the mode of genesis of the higher animals, but 

 after the construction of the microscope had been improved, 

 when, in fact, the compound microscope came into use, the 

 question of spontaneous generation was again brought promin- 

 ently forward. For the microscope revealed countless organisms 

 in ordinary water, but especially in infusion of animal and 

 vegetable substances, such as meat broth and an infusion of hay. 

 These organisms, or "infusoria," as they were called, are 

 characterised by their extreme minuteness ; hence the question 

 of their origin presented considerable difficulties. If we examine 

 an organic infusion recently prepared no sign of a living 

 organism is visible, but in a few hours the liquid teems with 

 myriads of minute beings. Whence have they come ? Are 

 they produced spontaneously from the animal or vegetable sub- 

 stances present in the infusion ? or are I hey the descendants of 

 pre-existing beings which have gained access to the infusion in 

 some way, are they formed from eggs or spores present in the 

 water or in the substances from which the infusions have been 

 made ? The English observer Needham was the first to attack 

 this problem experimentally. He argued that as heat destroys 

 both the seeds of plants and the eggs of animals a boiled infusion 

 ought not to develope any living organisms. He tried the 

 experiment, i.e., he heated the infusions in hermetically closed 

 vessels, and found that subsequently organisms did develope ; 

 hence he came to the conclusion that they were spontaneously 

 produced. After these experiments the Italian physician 



