A DEVICE FOR REGULATING THE TEMPERATURE OF 



INCUBATORS EITHER ABOVE OR BELOW ROOM 



TEMPERATURE. 



By JOHN H. NORTHROP. 



{From the Laboratories of The Rockefeller Institute for Medical Research) 



(Received for publication, January 23, 1920.) 



It is frequently desirable in studying the effect of temperature on 

 living organisms to have a convenient means of regulating the tem- 

 perature of an incubator or series of incubators within the range of 

 from 5-40°C. For this purpose it is essential to have a regulating 

 device which is reliable over long periods of time with a variation of 

 0.2-0.3°. As far as the author is aware no convenient method has 

 been described for this purpose. 



The device described in this paper has been in use continually for 

 several years and has proved rehable and accurate. It consists 

 essentially in regulating the flow of water through the jacket of a 

 double- walled incubator. This is accomplished, as shown in Fig. 1, 

 by causing a relay to direct a stream of water either through the 

 incubator or to waste as required by the temperature changes. This 

 is brought about by means of a wire D soldered to the armature of 

 the relay and attached at the other end to a glass pipette at the end 

 of a vertical rubber tube. The current necessary to move this wire 

 and pipette is so small that it is unnecessary to use a secondary circuit. 

 The relay is actuated directly by the same circuit which goes through 

 the regulator. With a relay of 150 to 200 ohms resistance, a potential 

 difference of about 1 volt is necessary. This may conveniently be 

 obtained from the ordinary lighting circuit by the use of lamps as 

 shown in Fig. 1. The regulator may be any convenient type, either 

 mercury-toluene or bi-metallic. It is placed in the regular position 

 in the incubator. 



The adjustment for temperatures higher than that of the room is 

 as follows: Hot water is allowed to run in a slow stream from the 



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