AN EFFICIENT ELECTRICAL INCUBATOR.* 



H. JOEL CONN and H. A. HARDING. 



SUMMARY. 



i. The ordinary form of gas-heated incubator is unsatisfactory 

 because of the danger of fire and the difficulty in securing constant 

 temperatures below that of the room. 



2. The difficulty has been avoided by constructing incubators 

 insulated with cork-board, heated by electricity, and one of them 

 cooled by the drip-water from a refrigerator. 



3. The cost of constructing four incubators, each of 7 cu. ft. 

 capacity, and a refrigerator of 25 cu. ft. capacity, was $382. 



4. The cost of maintenance, with the incubators at 18 , 25 , 30 , 

 and 37 C. respectively, and the refrigerator at 7 to io° C, is well 

 under $40 per year. 



INTRODUCTION. 



One of the necessities for careful bacteriological work is a means 

 of incubating cultures at various temperatures. Temperatures above 

 that of the room are easily secured, but satisfactory incubators 

 which remain constant at lower temperatures are almost unknown. 

 For this reason it seems worth while to describe a piece of apparatus 

 providing for incubation at both high and low temperatures, which 

 has been used here for a year with entire satisfaction. It consists 

 of a refrigerator and four incubators, and is heated by electricity. 



CONSTRUCTION OF REFRIGERATOR AND INCUBATORS. 



MATERIALS. 



In constructing the refrigerator and incubators the following 

 materials were employed. 



Lumber. The outer case was built of matched, seven-eighths-inch, 

 kiln-dried oak. In order to necessitate as few battens as possible, 

 and to furnish a smooth inner surface on which to lay the succeeding 

 layers of insulating material, strips of this oak were glued together 

 edge to edge, alternating the grain so as to prevent warping. Thus 

 each side of the case is essentially a single board. To protect the 

 wood from the action of dampness the inner surface was finished 

 with three coats of paint, while the outer was filled and varnished. 



* Reprint of Technical Bulletin No. 29, March, 1913. 



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