INTRODUCTION 2*J 



fusoria he believed to be nothing but these particles become 

 free. " The destruction of organized bodies is only a separation of 

 the organic particles of which they are composed. These particles 

 continue separate till they be again united by some active power. 

 When, however, a man's body has nearly attained its full size, he does 

 not require the same quantity of organic particles ; the surplus is, 

 therefore, sent from all parts into reservoirs destined for their recep- 

 tion. These reservoirs are the testes and seminal reservoirs " (page 

 397). " The different parts of the body are, however, built up of dif- 

 ferent kinds of organic units, so that upon disintegration there are 

 different forms of animalcula, which are in no respect different from 

 the spermatozoa of the same animal. The freed units are therefore 

 neither animals nor plants, but the formative elements of both. 

 Arising as the disintegrated parts of dead organisms, or rather as 

 elements which never die, they are organisms which pass from one 

 living state into another." This view was carried further by Need- 

 ham (1748), and as the Buffon-Needham hypothesis, was generally 

 accepted. Thus the early advocates of the theory of spontaneous gen- 

 eration did not maintain that living things arise from not-living sub- 

 stances, but that all organisms are derived from parts of those living 

 before, a sort of transmigration. Spallanzani, however, to whom so 

 much credit is due for our early knowledge of the Protozoa, adhered to 

 the view of Leeuwenhoek that the Infusoria are not the units which 

 constitute higher organisms, but distinct forms of life which, like other 

 organisms, are derived from definite germs. Furthermore, he vigor- 

 ously upheld their animal nature against Buffon and his school, 

 basing his arguments upon their voluntary movements, changes of 

 direction when moving, food taking, and upon their relations to 

 moisture and dryness, warmth and cold, to which they reacted like 

 higher animals. He found that Infusoria do not develop in a vacuum, 

 and must, therefore, come from germs contained in the air. Seeing 

 a Colpoda emerge from its cyst, he concluded that the cysts were 

 eggs, mistaking the cyst-case for the egg-membrane. He separated 

 the large from the small forms of Infusoria, a separation which was 

 the first attempt to distinguish the Protozoa from bacteria, and which 

 was destined to have great effect upon the theory of spontaneous 

 generation, for it is a significant fact that the forms which have been 

 supposed to arise by spontaneous generation have always been 

 those approaching the limits of vision. 1 



1 Spallanzani's work has hardly been sufficiently recognized by later writers. Never car- 

 ried away by enthusiasm, but describing only what he saw, he placed himself outside the 

 current of popular favor by opposing the tempting hypothesis of the nature-philosophers. 

 He seems to have combined his power of observation with a remarkable breadth of view, 

 which in some cases gave rise to daring conceptions. Thus, in 1776, he wrote: "Pour des 



