2 THE BIOLOGY OF BACTERIA 



was about forty years old, Holland had already given to the world 

 both microscope and telescope. Eobert Hooke did for England 

 what Hans Janssen had done for Holland, and established the same 

 conclusion that Leeuwenhoek arrived at independently, viz., that a 

 simple globule of glass mounted between two metal plates which 

 were 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 instru- 

 ment 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 " animalcula," 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 

 "animalcula." 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 disease. 

 Spallanzani, Pasteur, and Tyndall are the three workers who more 

 than others contributed to this discovery. Spallanzani was an Italian 

 who studied at Bologna, and was in 1*754 appointed to the Chair of 

 Logic at Eeggio. But his inclinations 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 demon- 

 strated 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 decompose. When, however, the flasks were but slightly 

 cracked, the air gained admittance, then invariably both organisms 

 and decomposition appeared. Schwann, the founder of the cell- 

 theory, and Schultze, both showed that if the air gaining access to 

 the flask were either calcined or drawn through strong acid the 

 result was the same as if no air entered at all, namely, there were no 

 organisms and there was no decomposition. The result of these investi- 

 gations was that scientific men began to believe that no form of 

 life arose de novo (aliogenesis), but had its source in previous life 

 (biogenesis). It remained for Pasteur and Tyndall to demonstrate 

 this beyond dispute, and to put to rout the fresh arguments for 

 spontaneous generation which Pouchet had advanced as late as 1859. 

 Pasteur collected the floating dust of the air, and found by means 

 of the microscope many organised particles, which he sowed on 

 suitable infusions, and thus obtained rich crops of "animalcula." 

 He also demonstrated that these organisms existed in varying 



