APPENDIX. 



THE short outline of bacteria and their products contained in the preced- 

 ing pages will not have had the effect desired if it does not induce in a 

 certain number of readers an ambition to undertake some experiments in 

 bacteriology, in at least some of its branches. As it is often extremely 

 difficult to obtain the most elementary knowledge of the technique of a 

 subject without being compelled to dive into elaborate and erudite articles, 

 it has been thought advisable to supplement the descriptions of methods 

 already given by a short resume of some of the simpler methods of experi- 

 mental investigation (the apparatus required for which is extremely simple, 

 and can be obtained at comparatively trifling cost), and to give a short 

 description of some of the commoner forms of bacteria that they may be 

 readily identified. 



HOT AIR STERILIZING APPARATUS. 



C. Salomonsen recommends a very inexpensive form of sterilizing oven in 

 which glass utensils, metal apparatus, wadding, paper, &c., may be heated 

 to about 150 C. It consists of an ordinary large-sized biscuit box, 

 such as may be obtained from any grocer. A round hole is cut in the 

 middle of the lid, and into this a cork is fitted to carry a thermometer 

 registering to 200 C. A small hole is punched in each of the four sides near 

 the top, and similar holes are made close to the bottom. On the bottom 

 of the box, inside, is fitted a piece of strong sheet iron, with the ends bent 

 at right angles to raise it about two-thirds of an inch, so that materials to 

 be sterilized do not touch the metal which is in immediate contact with the 

 flame. The lid is covered with a piece of felt, in the middle of which is a 

 hole for the thermometer. Another piece of felt, the breadth of which is 

 three-quarters the height of the box, and long enough to go round it out- 

 side, is fastened round the chamber, just below the upper, and above the 

 lower, air holes, and is kept in position with stout copper wire. The box 

 so prepared is supported on an ordinary tripod, between which and the box 

 rests a loose piece of thin sheet iron or tin (this latter prevents the burning 

 of the thin tin bottom of the box). Such a chamber may be heated by gas 

 or by a small oil stove. An ordinary cooking oven may also be used as a 

 hot air sterilizer. A more complicated apparatus is a double-walled sheet 

 iron box of about the same size as the above, or a little larger, with a hole 

 in the top to receive a thermometer, a door in front, and a movable bottom, 

 which can be easily renewed from time to time as it is burned through. All 

 objects placed in this sterilizing chamber must be protected against dust on 

 their removal. This is done in the case of flasks and test tubes with their 

 cotton wadding plugs by covering them with a layer or two of strong, hard, 



