lO PHARMACEUTICAL BACTERIOLOGY 



mentation was paved. In 1660 Leeuwenhoek discovered yeast cells. 

 From 1660 to 1760 the microscope was actively employed by a few investi- 

 gators, and additions were slowly made to the list of micro-organisms. 

 Audry (1761) designated microbes worms. Miiller of Copenhagen (1786), 

 grouped. them under two divisions, monas dind vibrio. In 1743 Henry 

 Baker, of England, pubhshed his work, "The Microscope Made Easy," 

 from which it would appear that very little progress had been made since 

 the time of Leeuwenhoek (1656). 



As early as 1686 Franceso Redi doubted that maggots were generated 

 de novo in putrid meats. He noticed that the presence of the maggots was 

 preceded by swarms of flies which, he concluded, had something to do with 

 the development of the maggots. He found that meat from which the flies 











n 



Fig. 2. — From Arcana Naturce. Cell structure of cork. Cell-lumen is shaded and cell- 

 walls are shown light. 



were excluded by means of paper or a very fine mesh wire screen, simply 

 decayed without any development of maggots. The paper cover and the 

 fine screen kept the eggs of the flies from being deposited on the meat, and 

 the meat was not infested by maggots, which, as Redi rightly conjectured, 

 developed from the eggs of the fly-like imago. This very simple but reli- 

 able experiment did much to create doubt as regards the correctness of -the 

 theory of spontaneous generation and other related beliefs. 



Spallanzani (1777) was among the first to demonstrate experimentally 

 that boiUng and hermetically enclosing,fermentable liquids prevented fer- 

 mentation. Ehrenberg (1828) discovered microscopic organisms in dust- 

 and in water, and in 1833 he classified all known bacteria under four orders, 

 bacterium, vibrio, spirillum, and spirocheta. Cagniard-Latour and 

 Schwann (1836) discovered the vegetable nature of yeast, and in 1837 

 Schwann declared that yeast was the direct cause of fermentative changes 

 resulting in the Uberation of alcohol and CO2, and that the causes of decay 

 were to be found in the atmosphere. BerzeUus (1827) declared that the 

 yeast cells were the direct cause of fermentation. F. Schulze (1836) pre- 

 vented decay in liquids containing certain organic substances by first heat- 



