CHAPTEE II 



PROTOZOA {COXTIXUED) : SPONTANEOUS GENERATION 



characters of protozoa classification 



The Question of Spontaneous Generation 



From the first discovery of tlie Protozoa, their life-history has 

 been the subject of the highest interest : yet it is only within 

 our own times that we can say that the questions of their 

 origin and development have been thoroughly worked out. If 

 animal or vegetable matter of any kind be macerated in water, 

 filtered, or even distilled, various forms of Protista make their 

 appearance ; and frequently, as putrefaction advances, form after 

 form makes its appearance, becomes abundant, and then disappears 

 to be replaced by other species. The questions suggested by such 

 phenomena are these: (1) Do the Protista arise spontaneously, 

 that is, by the direct organisation into living beings of the 

 chemical substances present, as a crystal is organised from a 

 solution: (2) Are the forms of the Protista constant from one 

 generation to another, as are ordinary birds, beasts, and fishes ? 



The question of the " spontaneous generation " of the Protista 

 was readily answered in the affirmative by men wlio l)elieved tliat 

 Lice bred directly from the filth of human skins and clothes ; ^ and 

 that Blow-fiies, to say nothing of Honey-bees, arose in rotten 

 flesh : but the bold aphorism of Harvey " omne vivum ex ovo " at 

 once gained the ear of the best-inspired men of science, and set 

 them to work in search of the " eggs " that gave rise to the 

 organisms of putrefaction. Piedi (ob. 1699) showed that Blow- 

 flies never arise save when other Blow-flies gain access to meat 

 and deposit their very visible eggs thereon. Leeuwenhoek, his 



' "We have ourselves had hard work to persuade intellii^cnt men of fair general 

 education, even belonging to a learned profession, tliat tliis is not the case. 



42 



