The History of the Subject 19 



Schulze worked, for, as was shown by those who repeated his 

 experiment, under the conditions that he regarded as certainly 

 excluding all hfe, germs can readily enter with the air. 



In 1838 Ehrenberg devised a system of classifying the minute 

 forms of life, a part of which, at least, is still recognized at the 

 present time. He, however, looked upon all forms of "infusorial 

 life" as animalculae or rrtinute animals, and Dujardin who wrote 

 about them in 1845 continued to do the same. The first to regard 

 some of them, notably the vibrios and spirilla of Ehrenberg, as 

 plant organisms, seems to have been Joseph Leidy who published a 

 paper in the Proceedings of the Academy of Natural Sciences of 

 Philadelphia in 1849 upon "^Entophyta or vegetal parasites infest- 

 ing the intestinal canal of animals," in which he held that the 

 organisms mentioned should be classed among the algce and placed 

 in the vegetable kingdom. 



Tyndall, stimulated by the work of Pasteur, conclusively proved 

 that the micro-organismal germs were in the dust suspended in the 

 atmosphere, and not ubiquitous in distribution. His experiments 

 were very ingenious and are of much interest. First preparing 

 light wooden chambers, with a large glass window in the front and a 

 smaller window in each side, he arranged a series of test-tubes in 

 the bottom, half in and half out of the chamber, and a pipet, working 

 through a rubber diaphragm, in the top, so that when desired the 

 tubes, one by one, could be filled through it. Such chambers were 

 allowed to stand until aU the contained dust had settled, and then 

 submitted to an optical test, to determine the purity of the contained 

 atmosphere, by passing a powerful ray of light through the side 

 windows. When viewed through the front, this ray was visible 

 only so long as there were particles suspended in the atmosphere to 

 reflect it. When the dust had completely settled and the light ray 

 had become invisible because of the purity of the contained atmos- 

 phere, the tubes were cautiously filled with urine, beef-broth, and a 

 variety of animal and vegetable broths, great care being taken that 

 in the manipulation the pipet should not disturb the dust. Their 

 contents were then boiled by submergence in a pan of hot brine 

 placed beneath the chamber, in contact with the projecting ends of 

 the tubes, and subsequently allowed to remain undisturbed for 

 days, weeks, or months. In nearly every case hfe failed to develop 

 in the infusions after the purity of the atmosphere was established. 



n. CHEMIC CONTRIBUTIONS; FERMENTATION AND PUTREFACTION 



As in the world of biology the generation of hfe was an all- 

 absorbing problem, so in the world of chemistry the phenomena of 

 fermentation and putrefaction were inexphcable so long as the 

 nature of the ferments was not understood. 



In the year 1837 Latour and Schwann succeeded in demonstrating 

 that the minute oval bodies which had been observed in yeast since 



