18 INTRODUCTION 



pigment (chlorophyll), which implies an analytical or destructive 

 function in the economy of Nature. 



The great majority of bacteria are saprophytic, living upon dead 

 organic matter, which they transform into simple compounds suitable 

 for plant use. These bacteria are Nature's analysts. Some are para- 

 sitic on living plants and animals; a few are progressively pathogenic 

 for man and animals. It is this last group, few in numbers, but for- 

 midable in that their activities are in partial opposition to those of 

 man and animals, that has given to bacteria all the notoriety which 

 they possess. 



Anton von Leeuwenhoek, a Dutch spectacle maker, appears to have 

 been the first to see bacteria: in 1675, with lenses of his own grinding, 

 he examined various putrescent fluids, drops of water, scrapings from 

 his teeth, and his own diarrheal discharges. He says in his writings, 

 collected and edited by Robert Hooke, 1 "With great astonishment 

 I observed everywhere through the material which I was examining, 

 animalcules of the most minute size, which moved themselves about 

 very energetically." It is possible to recognize cocci, bacilli and 

 spirilla in his drawings, and it is almost certain that he actually observed 

 motility among his organisms. The learned monk, Athanasius Kircher, 

 observed and described "minute living worms" as early as 1659, but 

 his optical equipment was inferior to that of .von Leeuwenhoek and it 

 is doubtful if he actually saw bacteria. 



Improvements in the microscope opened a new world for investiga- 

 tion and speculations concerning the doctrine of the Spontaneous 

 Generation of Life led to numerous experiments of increasing refine- 

 ment that finally resulted in the brilliant researches of Pasteur, and 

 Tyndall, who showed by numerous ingenious and carefully executed 

 experiments that the phenomena in putrescible fluids erroneously 

 interpreted as spontaneous generation did not take place when proper 

 precautions in manipulation were observed. About 1835 achromatic 

 lenses for the microscope reached a state of perfection compatible 

 with the examination of minute objects and the microscope was almost 

 immediately applied to the study of various morbid processes, with 

 remarkable success. Bassi (1837) discovered a fungus which caused 

 a contagious disease of silk worms known as muscardine; Cagniard 

 de Latour and Schwann observed and described the yeast plant in 

 liquids undergoing alcoholic fermentation. 



1 Collected Memoirs of Anton v. Leeuwenhoek, Royal Society of London, 1675, 1683. 



