THE CULTIVATION OF BACTERIA. 87 



A form of incubator devised by Rogers* for this purpose 

 consists of a refrigerator or of a specially constructed chamber 

 heated by electricity and controlled by an electric thermoregu- 

 lator. Below is given a description of an incubator constructed 

 according to Rogers' plans. This incubator has been in use 

 for some time and has given entire satisfaction since the pre- 

 cautions noted below were followed. There would appear 

 no reason why this incubator should not be employed for high 

 temperatures as well for low, but so far it has been run at 22 C. 

 The temperature has kept very constant. The incubator 

 consists of a refrigerator, 30 inches high, 24 inches wide, 18 

 inches from front to back, all outside measurements. Instead 

 of the ordinary drip pipe, there is a coil of i-inch galvanized 

 iron pipe run down the back of the cooling chamber attached 

 water-tight to the ice tank. From the bottom of the cooling 

 chamber the coil runs up perpendicularly nearly to the 

 bottom of the ice compartment, and then runs horizontally 

 through the wall of the refrigerator. A bracket on the outside 

 supports a drip-pan. A thermometer encased in a finestrated 

 metal jacket is inserted about half way up on one side. A 

 lump of ice, about 50 pounds, placed in the ice compartment 

 serves to keep the temperature sufficiently cool. In summer 

 doubtless more ice will be required. 



For heating, an ordinary, i6-candle-power electric bulb is 

 used, and the electricity is obtained from the public supply. 

 The wire is run through one of the walls, and a part of the 

 current is made to operate a horse-shoe magnet, and another 

 part is conducted through the lamp used for heating. 



The accompanying diagram, (Fig. 27), will serve to show 

 the arrangement. 



A telegraph key is used to supply the horse-shoe magnet 



*L. A. Rogers. On electrically controlled low temperature incubators. 

 Centralblatt fur Bakteriologie, etc. Bd. XV. Abt. II. Double No. 7-8. pp . 

 236-239. Sept. 23, 1905. 



