Pathogenic micro-organisms : including bacteria and Protozoa; a practical manual for students, physicians and health officers / by William Hallock Park ; assisted by Anna W. Williams.
- William Hallock Park
- Date:
- 1908
Licence: In copyright
Credit: Pathogenic micro-organisms : including bacteria and Protozoa; a practical manual for students, physicians and health officers / by William Hallock Park ; assisted by Anna W. Williams. Source: Wellcome Collection.
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![with the air admitted the hoiled solutions quickly putrefied, and liv- ing oi'ganisms were found to he ju’esent. Schwann in 1839 obtained similar results in another Avay; he deprived of microorganisms the air admitted to his hoiled liquids hy passing it through a tube which was heated to a teinjKU-ature high enough to destroy them. To this investigator is also due the credit of having discovered the specific cause—the yeast ])lant, or mccharo- myces cerevisice—of alcoholic fermentation, the ])rocess hy which sugar is decomposed into alcohol and carbonic acid. Again, it was objected to these experiments that the heating of the air had perhaps brought about some chemical change which hindered the production of fermentation. Schroeder and von Dusch in 1854 then showed that by a simple process of filtration, which has since proved of inestimable value in bacteriological work, the air can be mechanically freed from germs. By placing in the mouth of the flask containing the boiled solutions a loose plug of cotton, througb which the air could freely circulate, it was fouud that all sus])ended microorganisms could be excluded, and that air passed through such a filter, whether hot or cold, did not cause fermentation of boiled infusions. Similar results were obtaiucd by Hoffmaun in 1860, and by Chev- renl and Pasteur in 1861, without a cotton filter, by drawing out the neck of the flask to a fine tube aud turning it downward, leaving the mouth open. In this case the force of gravity prevents the suspended bacteria from ascending, as there is no current of air to cariw them upward through the tube into the flask containing tlie boiled iufusiom Tyndall later showed (1876), by his well-known investigatious upon the floating matters of the air, that in a closed chambei, in which the air is not disturbed by currents, all suspended particles settle to the bottom, the superincumbent air being optically pure, as is proved by passing a ray of light through it. lie demonstrated that the presence of living organisms in decomposing fluids was always to be explained either by the preexistence of similar living forms in the infusion or upon the walls of the vessel containing it, or b^ t le infusion having been exposed to air which was contaniinatcc vit i organisms. , These facts have since been practically confirmed on a large scale in the preservation of food by the process of sterilization. Indeed, there is scarcely any biological iiroblem wbich has been so satisfac- torily solved or in which such iiuiform results have been obtained ; but all through the experiments of the earlier investigators irregulari- ties were constantly appearing. Although iii the huge lua.ioiity o cases it was found possible to keep boiled organic liquids sterile lu flasks to wbich the oxygen of the air bad free access, the question ot spoutaucous geiieratioii still remained unsettled, iiiasmiici as sioually, even under the most careful ]u-ecautious, dewiu|iositiou did occur ill such boiled liquids. . . i This fact was explained by Bastcur in 1860 by experiments show-](https://iiif.wellcomecollection.org/image/b28137541_0022.jp2/full/800%2C/0/default.jpg)
