BACTERIOLOGICAL APPARATUS 59 



When incubators are heated by electricity, the temperature 

 is controlled by electric thermostats. When gas is used, the 

 metallic bar regulators seem to give the best results and to 

 require the least attention. 



Special apparatus. The special apparatus necessary 

 depends upon the kind of work that is being done. In the 



Fig. 24. 



Fig. 25. 



Fig. 24. An apparatus used by Erwin F. Smith for cultivating 

 anaerobes. Into one end of a large U tube place about three grams 

 of dry pyrogallic acid and three grams of sodium hydrate. Close 

 this end with a rubber stopper and pour about 15 cc. of water into 

 the other end (b) holding the U tube so that the water all escapes 

 into the branch (a) containing the reagents. Now insert in the 

 second branch (b) a small test tube (c) containing the inoculated 

 medium and a loose cotton plug. Close this end of the U tube with 

 a rubber stopper and stand the U tube in a beaker (d) containing 

 mercury or glycerin. Good results were obtained by this method. 



Fig. 25. Fermentation tube. This tube was introduced by 

 Theobald Smith for the study of anaerobic bacteria. Strictly anae- 

 robes multiply in the closed branch only. 



bacteriological examination of liquids or semi-solids, it is 

 frequently desirable to centrifuge the material. For this, 

 a centrifuge is required. The size is to be determined by 

 the nature of the work to be done. In the study of toxins, 

 bacterial filtrates and the like, it is necessary to have filter- 



