2 BACTERIA 



conclusion that Leeuwenhoek arrived at independently, viz., 

 that a simple globule of glass mounted between two metal 

 plates and pierced with a minute aperture to allow rays of 

 light to pass was a contrivance which would magnify more 

 highly than the recognised microscopes of that day. It was 

 with some such instrument as this that the first micro- 

 organisms were observed in a drop of water. It was not 

 until more than a hundred years later that these " animal- 

 cules," as they were termed, were thought to be anything 

 more than accidental to any fluid or substance containing 

 them. Plenciz, of Vienna, was one of the first to conceive 

 the idea that decomposition could only take place in the 

 presence of some of these "animalcules." This was in the 

 middle of the eighteenth century. Just about a century later, 

 by a series of important discoveries, it was established beyond 

 dispute that these micro-organisms had an intimate causal 

 relation to fermentation, putrefaction, and infectious diseases. 

 Spallanzani, Pasteur, and Tyndall are the three who more 

 than others contributed to this discovery. Spallanzani was 

 an Italian, who studied at Bologna, and was in 1754 

 appointed to the chair of logic at Reggio. But his inclin- 

 ations led him into the realm of natural history. Amongst 

 other things, his attention was directed to the doctrine of 

 spontaneous generation^ which had been propounded by 

 Needham a few years previously. In 1768 Spallanzani 

 became Professor of Natural History at Pavia, and whilst 

 there he demonstrated that if infusions of vegetable matter 

 were placed in flasks and hermetically sealed, and then 

 brought to the boiling point, no living organisms could 

 thereafter be detected, nor did the vegetable matter decom- 

 pose. When, however, the flasks were very slightly cracked, 

 and air gained admittance, then invariably both organisms 

 and decomposition appeared. Schwann, the founder of the 

 cell-theory, and Schulze, both showed that if the air gaining 

 access to the flask were either passed through highly heated 



