The microscope : its history, construction, and application, being a familiar introduction to the use of the instrument, and the study of microscopical science / by Jabez Hogg.

Hogg, Jabez, 1817-1899.

Date:: 1898

Credit: The microscope : its history, construction, and application, being a familiar introduction to the use of the instrument, and the study of microscopical science / by Jabez Hogg. Source: Wellcome Collection.

Provider: This material has been provided by University of Bristol Library. The original may be consulted at University of Bristol Library.

401/780 (page 365)

$SIZE OF PATHOGENIC FUNGI. substances which arc the refuse of life—such material is promptly seized upon by micro-organisms, by means of which histolysis is rapidly accomplished. Bacteria require a power of from 600 to 1,000 diameters or more for the determination of the species to which they belong. The number of species has been so much increased of late that a bulky volume is found to be insufficient for their enumeration. I am, however, by the courtesy of Professor Crookshank, enabled to present my readers with the typical forms of thirty-nine species of Bacteria, Schizoniycetes, or fission-fungi, a selection, it will be seen, chiefly taken from among pathogenic organisms—those believed to originate disease. But many of the supposed Saprophytic forms often described as originating disease are merely accidental associates, that is, living in companionship for a time. Size.—In ordinary terms of measurement, bacteria are on an average from ■25^00*'^ about s^^th of an inch long. These measurements do not convey a definite impression to the mind. It is calculated that a thousand million of them could be contained in a space of ^th of an inch. The best impression of the size of the bacteria is, perhaps, obtained when it is stated that a ■^^-Ya.c\\ immersion objective gives a magnification of nearly 2,200 diameters, and that under this power the bacteria appear to be about the size of very small print. The standard of measurement accepted by bacteri- ologists is the micro-millimeter. One millimeter is equal to about 2 5000^^ English inch. The number of micrococci in a milli- gramme of a culture of Stap)hylococcus pyogenes aureus has been estimated by Bujwid by counting at eight thousand millions. Not only do various species difi'er in dimensions, but considerable differ- ences may be noted in a pure culture of the same species. On the other hand, there are numerous species which so closely resemble each other in size and shape that they cannot be diflferentiated by microscopic examination alone, and we have to look to other charac- teristics, as colour, growth in various culture media, pathogenic power, chemical products, (fee, in order to decide the question of identity. Rejyfoduction.—The reproduction of bacteria takes place for the most pai't by fission and by spore formation. Fissioii is a process of splitting up or division, whereby an oi'ganism divides into two or more parts, each of which lives and divides in its turn. If$