Page:Science vol. 5.djvu/538

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��— 120° C. Agar-agsr icill stajid ajiy amouiiL of pro- loDged beat.

The pot In which the sterilization is done lias three openings (fig.!). One is for ILe s«fety-v(Uve; the eecond, for the tbermo meter, has a tube closed at the bottom to prevent preuure upon tbis inalrument; and the third la conical, ctoaed with a corlt kept in place by a handle and thumb-acrew. A metallic tube,

Accidental contamination is the one thing to be avoided in these proceedings, which is attained by heating every thing used for sowing, etc. to 300° C; the objection to this being the difficulty of getting tbe instruments cool enough not to destroy the germs which we wish to use, and at the same time not cool enough to take in impurities. Manual dexterity teaches much, but more rigorous measures are better still. I first sterilize all my instruments in test-tubes with flax stoppers, through which they pass. Such glass pipettes, pointed, with an opening at the

��bent twice, passes into the chamber. The free end isconnectedbyruliber tubing, kept closed by a spring, to a short metal tube with a trocar point, and an open- ing near the extremity in the side.

After the fluid has been sufficiently sterilized, upon introducing the bent tube into the upper part of the chamber, and opening the spring, the vapor is forced one Allow it to run for a few moments, heat the of the tube, work this through the cotton stopper of a sterllixed flask, and the nutrient fluid will be gradu- ally passed over into the flask.

To obviate the difficulties in the way of piercing the ordinary cotton plug with safely, small test-tubes with a flaring mouth, and a hole in the l>ottoni, are placed In the mouths of the fiasks, with cotton outside and flax at their bottoms. Above the llai is a plug of cotton (fig. Fio. i. — (!oNic*i, 2). The trocar point can be easily RDLTDM-rusK. forccd through the flax and the thin layer of cotton underneath, if the upper plug be removed (tig. 3) ; ai)d this method seems to offer the easiest and most certain manner of filling the flasks or other vessels. For cultures, I prefer test-tubes placed in racks of iron wire (fig.

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��' conical flasks with flat bottoms {lig. G|.

��side, and plugged at the other end with cottoti-wool or flax (fig. 6, A). When in use, this end has a rub- ber cup over it, by means of which the floid may be drawn up or expelled. For more solid materials, I use knitting-needles, or platinum wire in slrai^l tubes with open bevelled ends |flg.e,JJ), and,foraoir- Ing, push the point of the needle through the open end of the tut>e. In trausferriug a pure culture froD) one flask to another, these means are sufficient; bat, with mixed cultures, separation of the various forma must be accomplished, which ma; be done by cultun fluids or nutrient gelatine. For fractional cultures in liquids, the priadpt}

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