. Carnegie Institution of Washington publication. PREPARATION OF POURED PLATES. 105 The agar may be poured at 42° C. in case of organisms whose thermal death- point is known to be high (50° C. or above). For all others it must be cooled carefully to 40° C. before inoculating for poured plates. This requires five or six minutes in the water bath at 40° C. Even this temperature is too high for some organisms and then gelatin at 30° C. may be used. When ready to pour, take a clean absorbent cloth and carefully wipe all water from the outside of the tube (the lips of which have been previously fla
. Carnegie Institution of Washington publication. PREPARATION OF POURED PLATES. 105 The agar may be poured at 42° C. in case of organisms whose thermal death- point is known to be high (50° C. or above). For all others it must be cooled carefully to 40° C. before inoculating for poured plates. This requires five or six minutes in the water bath at 40° C. Even this temperature is too high for some organisms and then gelatin at 30° C. may be used. When ready to pour, take a clean absorbent cloth and carefully wipe all water from the outside of the tube (the lips of which have been previously flamed gently with a rotation of the tube on its long axis), lift the cover of the dish only as much as is necessary', hold the cover over the dish (not at one side), pour quickly but gently, and re-cover, tilting the dish about quickly but gently, if the fluid has not already covered the bottom. To en- tirely cover the bottom sometimes reqxiires a smart little jeik, if the agar is not very fluid. The student must learn to work rapidly and dextrously, then there will be no complaint that the agar has solidified before the plates are poured. The plates should be set on a level shelf while the agar or gelatin is hardening, or, if the colonies per square centimeter are to be determined, a nivelling appa- ratus such as that shown in fig. 66 must be used, and the dishes should have flat bottoms. When plates have been inoculated too abundantly to secure subcultures from single colonies, these may some- times be obtained from the traces of agar or gelatin left in the tubes from which the plates were poured. With this end in view, these tubes should be re- plugged and laid away, for a few days, the lips and top of the tube which were wet by the agar or gelatin being first heated hot in the flame, care being exer- cised not to crack the tubes. All tubes containing fluids should be opened and inoculated in a position as nearly horizontal as their contents will permit, and tubes of soli
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