10 PHARMACEUTICAL BACTERIOLOGY. 



microbes of the mouth cavity, infusoria of stagnant water and cellular 

 structure of vegetable tissues. He observed the motion of bacteria and in- 

 fusoria, made measurements, illustrated capillary circulation in the web 

 of the frog's foot, etc. He was closely followed by Robert Hooke, who 

 published his Micrographia in 1658. The discoveries of Leeuwenhoek 

 and Hooke were certainly epoch-making. A new world of minute organisms 

 was made known, the question of spontaneous generation received a new 

 turn, and the way to the discovery of the causes of disease and fermentation 

 was paved. In 1660 Leeuwenhoek discovered yeast cells. From 1660 to 

 1760 the microscope was actively employed by a few investigators, and addi- 

 tions were slowly made to the list of micro-organisms. Audry (1701) desig- 

 nated microbes worms. Muller, of Copenhagen (1786), grouped them 

 under two divisions, monas and vibrio. In 1743 Henry Baker, of England, 

 published his work, "The Microscope Made Easy," from which it would 

 appear that very little progress had been made since the time of Leeuwen- 

 hoek (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 

 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 boiling 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 von 

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

 Schwann decleared that yeast was the direct cause of fermentative changes 

 resulting in the liberation of alcohol and CO 2 , and that the causes of decay 

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

 cells were the direct cause of fermentation. F. Schulze (1836) prevented 

 decay in liquids containing certain organic substances by first heating or 

 boiling them and excluding the air by means of a layer of oil or by closing 

 the container with cotton and supplying it with air which had been ster- 

 ilized by passing through sulphuric acid. Braconnot (1831) advanced the 

 theory that yeast cells had the power of holding, and condensing within the 



