Volume 17

Twentieth century practice : an international encyclopedia of modern medical science / by leading authorities of Europe and America ; edited by Thomas L. Stedman.

Date:
1895-1903
Catalogue details

Licence: In copyright

Credit: Twentieth century practice : an international encyclopedia of modern medical science / by leading authorities of Europe and America ; edited by Thomas L. Stedman. Source: Wellcome Collection.

    25/736 (page 11)
    bacilli may iive for weeks or months. Thus I found scrapings from a dry bit of membrane to contain vigorous living bacilli for a period of four months after removal from the throat, and I believe if the membrane had not been at that time completely used, living bacilli could have been obtained for a much longer period; in culture media when kept at the blood heat they usually die after a few weeks or months, but under certain conditions, as when sealed in tubes and protected from heat and light, they retain their virulence for years. The bacillus is not sensitive to cold under ordinary conditions, and retains its virulence after freezing. It begins to develop, but grows slowly, at a temperature of 20° C., or even less. It grows more rap- idly as the temperature rises, and attains its maximum development at 37° C. It may grow at a temperature as high as 41° C. and retain its virulence for months. Growth on Blood Serum,.— Loeffler’s blood-serum mixture (see p. 37) is the most favorable medium for the growth of the diphtheria bacillus, and is used particularly for diagnostic purposes in examining cultures from the throats of persons suspected of having diphtheria. If we examine the growth of the diphtheria bacillus in pure culture on blood serum, we shall find at the end of from ten to twelve hours small colonies of bacilli, which appear as pearl-gray, whitish-gray, or more rarely yellowish-gray slightly raised points. The colonies when separated from each other may increase in forty-eight hours so that the diameter may be one-eightli of an inch. The borders are usually somewhat uneven. The colonies lying together become confluent and fuse into one mass, especially if the serum be rather moist. During the first twelve hours, the colonies of the diphtheria bacilli are about equal in size to those of the other pathogenic bacteria which are often present in the throat; but after this time the diphtheria colonies become larger than those of the streptococci and smaller than those of the staphylococci. The diphtheria bacilli in their growth never liquefy the blood serum. Growth on Agar.—On one per cent, slightly alkaline plain nutrient or glycerin agar the growth of the diphtheria bacillus is less certain and luxuriant than upon blood serum; but the appearance of the colo- nies when examined under a low-power lens, though very variable, is often far more characteristic. The diphtheria bacillus obtained from old laboratory cultures grows well as a rule on suitable nutrient or glycerin agar, but when fresh from pseudomembrane it frequently grows on these media with great difficulty, and the colonies develop so slowly as to be covered up by the more luxuriant growth of other bacteria, or fail to develop at all. Since the growth of some of the associated bacteria in pseudomembranes produces acid in the media,