Bacteriology.

  • International Congress of Hygiene and Demography.
Date:
1892
Catalogue details

Licence: Public Domain Mark

Credit: Bacteriology. Source: Wellcome Collection.

Provider: This material has been provided by London School of Hygiene & Tropical Medicine Library & Archives Service. The original may be consulted at London School of Hygiene & Tropical Medicine Library & Archives Service.

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    is partly due to the increased rapidity of the hot draught coming from the warm chamber, which prevails when the external temperature becomes lower, and partly to the condensation of steam taking place on the sides of the bell jar. This regulation is aided by replacing the inverted basin used for sterilisation by one not perforated at the sides (Fig. 1), so that when the temperature falls within the incubator the water is drawn into this small chamber, and as this small chamber is situated immediately above the light, it becomes rapidly hotter. Immediately, however, that the temperature rises again, the water passes again out of this basin or capsule. It is, of course, important that the lowermost cultivations should be separated from this regulating chamber by a certain amount of space, so that the lowermost moist chamber must not be made to rest directly on the bottom of the inverted basin; for this reason I usually fix to the glass plate forming the bottom of the moist chambers three or four pieces of cork. In thi.s way the temperature of each moist chamber is rendered more independent of the metallic parts through which heat might be conducted (Fig. 1). Nothing of course prevents the use of an ordinary heat regulator and of gas with this apparatus, but as I offer it not to replace the more perfect forms of incubator, but simply as a sufficiently reliable and cheap apparatus readily applicable to a great variety of experiments for which the larger incubators are not suitable, owing to their bulk, their expense and difficulty of adaptation,* I will not attempt to show how my incubator might be advantageously complicated. I may add that the temperature of the upper part of the incubator is always lower thanthat of the lower part; the difference varies according to the size of the chambers, but is usuall}'^ about 5° C.f I therefore place in each incubator two moist chambers. The temperature of each chamber is ascertained by means of a maximum thermometer placed within the chamber itself. The form of moist chamber I have devised is convenient for use tvith this incubator, and takes less room than the usual form. The condensed water is also less liable to drop on the objects placed in the chamber. The chamber itself is composed of a glass plate coveted with a flat bottomed basin or crystallizer (Fig. 1). The glass plate is covered with two or three rounds of filter paper, over which a flat capsule containing a solution of corrosive sublimate (1 in 1,000) is inverted. In this way the filter paper is constantly kept moist. The capsules used for cultivations are more easily handled when placed in small frames made of two bands of zinc soldered together at each end so as to enclose the capsule. In this way they can be piled on the top of each other, and any one removed without disturbing * My later experiments on pathogenic moulds and on psorospermosis were all made by means of these incubators. By using two concentric bell jars separated by a small interval, it is easy to render the temperature more uniform all through the incubator. I have used this disposition several times, but have not found it necessary in most cases. The same arrangement allows a higher degree of heat to be obtained in the steriliser also Ifig. 9).