502 



SCIENCE, 



[Vol. V., No. 124. 



— 120° C. Agar-agar will stand any amount of pro- 

 longed heat. 



The pot in which the sterilization is done has three 

 openings (fig. 1). One is for the safety-valve; the 

 second, for the thermometer, has a tube closed at the 

 bottom to prevent pressure upon this instrument; 

 and the third is conical, closed with a cork kept in 

 place by a handle and thumb-screw. A metallic tube, 



Fig. 4. — Rack fob preservation tubes. 



bent twice, passes into the chamber. The free end 

 is connected by rubber 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 

 out. Allow it to run for a few moments, heat the 

 trocar end of the tube, work this through the cotton 

 stopper of a sterilized 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 safety, small 

 test-tubes with a flaring mouth, 

 and a hole in the bottom, are 

 placed in the mouths of the 

 flasks, with cotton outside and 

 flax at their bottoms. Above 

 the flax is a plug of cotton (fig. 

 2). The trocar point can be easily 

 forced through the flax and the 

 thin layer of cotton underneath, 

 if the upper plug be removed (fig. 3) ; and 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. 

 4), or conical flasks with flat bottoms (fig. 5). 



Fig. 5. — Conical 

 culture-flask. 



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 

 the 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 vigorous measures are better 

 still. 



I first sterilize all my instruments in test-tubes 

 with flax stoppers, through which they pass. Such 

 are glass pipettes, pointed, with an opening at the 



Fig. 6. — Pipette 

 and platinum 



NEEDLE. 



Fig. 7. — Graduated bubette. 



side, and plugged at the other end with cotton- wool 

 or flax (fig. 6, J.). When in use, this end has a rub- 

 ber cup over it, by means of which the fluid may be 

 drawn up or expelled. For more solid materials, I 

 use knitting-needles, or platinum wire in straight 

 tubes with open bevelled ends (fig. 6, B), and, for sow- 

 ing, push the point of the needle through the open 

 end of the tube. In transferring a pure culture from 

 one flask to another, these means are sufficient; butj 

 with mixed cultures, separation of the various forms 

 must be accomplished, which may be done by culture 

 fluids or nutrient gelatine. 

 For fractional cultures in liquids, the principal 



