2 HISTORICAL OUTLINE 



the middle of the nineteenth century. The pure bacteriologist of the future will 

 owe a lasting debt to those who have worked on the applied side, and his investi- 

 gations will necessarily be based upon the knowledge gained by the medical or 

 agricultural bacteriologist. The study of immunology, for instance, has supplied 

 a body of facts, and an armoury of technical methods, which no bacteriologist 

 can neglect, and which will inevitably give to future bacteriological research 

 certain peculiarities of outlook and special methods of attack. 



It is customary, in summarizing the history of bacteriology, at least in relation 

 to medicine, to refer to the conception advanced by Fracastorius of Verona (1546), 

 concerning a contagium vivum as the possible cause of infective disease, and to the 

 views advanced by von Plenciz (1762) on the specificity of disease, based on a belief 

 in its microbial origin. A concrete science is, however, seldom advanced to any 

 considerable extent by arguments, however ingenious, which are propounded with- 

 out appeal to experiment, or to wide and detailed observation ; and the absence of 

 all real progress until the middle of last century is sufficient evidence that the views 

 of Fracastorius, von Plenciz and others have acquired their main significance from 

 knowledge gathered by later generations, rather than from their inherent fertility. 

 The construction and use of the compound microscope was an essential pre- 

 requisite to the study of microbial forms, and the reported observation by Kircher 

 (1659) of minute worms in the blood of plague patients forms, perhaps, the earliest 

 attempt at direct microscopical observation in this field. It is, however, more than 

 doubtful whether Kircher could have seen plague bacilli, or indeed any bacterial 

 forms, with the apparatus which he had at his disposal. To van Leeuwenhoek 

 (1683) must be ascribed the credit of placing the science of microbiology on the firm 

 basis of direct observation (Dobell 1932). This Dutch maker of lenses developed 

 an apparatus and technique (Cohen 1937) which enabled him to observe and 

 describe various microbial forms with an accuracy and care which still serve as 

 a model for all workers in this field. He observed, drew, and measured with 

 considerable approximation to truth large numbers of minute living organisms, 

 including bacterial and protozoal forms. It is, perhaps, somewhat surprising that 

 this marked advance was not followed by further rapid progress in our knowledge 

 of bacteria and their activities. Such progress was, however, impossible without 

 further developments in technique. The world of minute living things, opened 

 to morphological study by van Leeuwenhoek, was seen to be peopled by a multi- 

 tude of dissimilar forms, whose interrelationships it was impossible to determine 

 without preliminary isolation ; and, so far as bacteria were concerned, this isolation 

 was not accomplished until the problem of artificial cultivation was solved, almost 

 two hundred years later. 



The real development of bacteriology as a subject of scientific study dates 

 from the middle of the nineteenth century, and is the direct outcome of the work 

 of Louis Pasteur (1822-95). Isolated observations of microbial parasites, by 

 Brassi, PoUender, Davaine and others, have priority in particular instances, just 

 as Schultze, Schroeder and Dusch and others initiated technical methods which 

 Pasteur applied to his own researches. But it was Pasteur and his pupils who 

 settled the fundamental questions at issue, and developed a technique which made 

 possible the cultivation and study of bacteria. 



Trained as a chemist, Pasteur was led to the study of microscopic organisms 

 by his observations on the phenomena of fermentation. His early studies on the 

 structure of the tartrates, and on molecular asymmetry, had led him to believe 



