. Pathological technique; a practical manual for workers in pathological histology and bacteriology. species is that known as the plate method of Petri. This isa modification of the original complicated method of Koch. The method consists in making dilutions in meltedagar-agar or gelatin tubes, and then pouring the infectedmedium into shallow glass dishes (Fig. 21) previously steril-ized, in which it is allowed to solidify. A few bacteria arethus distributed throughout a thin layer of culture-medium CULTURE METHODS. 219 in the dilutions, and the colonies which develop from themare then more or
. Pathological technique; a practical manual for workers in pathological histology and bacteriology. species is that known as the plate method of Petri. This isa modification of the original complicated method of Koch. The method consists in making dilutions in meltedagar-agar or gelatin tubes, and then pouring the infectedmedium into shallow glass dishes (Fig. 21) previously steril-ized, in which it is allowed to solidify. A few bacteria arethus distributed throughout a thin layer of culture-medium CULTURE METHODS. 219 in the dilutions, and the colonies which develop from themare then more or less separated from one another, so thatpure cultures may be obtained from them. In carrying outthis method the procedure is as follows: Three sterile gelatin or agar-agar tubes are melted by heatand placed in a water-bath warmed to between 400 and 42°C. for several minutes, to bring the culture-medium to thistemperature. This temperature is important especially in thecase of agar-agar, for it is just above the solidifying point ofthat medium (38° C.) and yet not injurious to the vitality of. FIG. 21.—Petri dish with colonies. the bacteria. The tubes are then infected successively fromthe bacterial growth or from the pathological material fromwhich it is desired to obtain discrete colonies, in the samemanner as described for the method with blood-serum tubes—viz. one tube being inoculated from the growth or tissue,a second tube or dilution from the first tube, and a third tubeor dilution from the second tube, the platinum wire beingsterilized after each inoculation. For making the dilu-tions a platinum wire bent into the form of a small loop(see page 213) is to be used, and as much of the culture-fluidas will adhere to it used for inoculating. The wire shouldbe moved back and forth several times in the medium of eachtube when inoculating it, in order to ensure a good distribu-tion of the bacteria throughout the fluid. The contents ofeach tube thus inoculated are then pou
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