. Public health laboratory work, including methods employed in bacteriological research, with special reference to the examination of air, water and food contributed . e may be used. Sometimes it is advisable, as inthe case of actinomyces and tubercle, to use a narrowspatula, in order to thoroughly crush iip the growthwhen inoculating. Incubators.—Incubators are well insulated cham-bers (fig. no) surrounded by either a jacket of air orwater; by means of a heat regulator they can be main-tained at a constant temperature. Much depends upon the form of regulator used. Amost useful and non-breakab
. Public health laboratory work, including methods employed in bacteriological research, with special reference to the examination of air, water and food contributed . e may be used. Sometimes it is advisable, as inthe case of actinomyces and tubercle, to use a narrowspatula, in order to thoroughly crush iip the growthwhen inoculating. Incubators.—Incubators are well insulated cham-bers (fig. no) surrounded by either a jacket of air orwater; by means of a heat regulator they can be main-tained at a constant temperature. Much depends upon the form of regulator used. Amost useful and non-breakable form is the horse-shoemetal regulator which was early used in the physiologicallaboratory of University College, London, and hassince been adopted by M. Roux in the Pasteur Insti-tute. A common form is the well known mercuryregulator; it is, however, very liable to break, and thenif the mercury comes in contact with the copper work 446 LABORATORY WORK. of the incubator, very considerable corrosion is theresult; another form is the membrane regulator usedby DArsonval, in which the expansion of a column ofwater presses an india-rubber or thin copper membrane. Fig. iio.—Incubator. against the gas inlet. Where gas is not available, oil orthe heat of a greenhouse may be used. It is often veryuseful, as well as easy, to maintain a small room at atemperature of 20° C. by means of hot water pipes orby one of the numerous forms of patent stoves. As METHODS OF CULTIVATION. 447 soon as the tubes in the incubator have well startedgrowing they should be removed, for as before ex-plained the media tend to become dry. Drop cultures.—This is a most useful form ofcultivation and one which was much used by thepioneers of bacteriology. By its means the growth ofthe organisms can be studied under the is necessary to have several micro-slides, hollowedin the centre, or slides to which glass rings, varyingfrom the -^-^ to -|- in., are firmly cemented (to withstandheat and moi
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