UNITED STATES DEPARTMENT OF AGRICULTURE 
{ BULLETIN No. 951 
Contribution from the Bureau of Animal Industry 
JOHN R, MOHLER, Chief 
4^ 
Washington, D. C. 
PROFESSIONAL PAPEK 
lune 4, 1921 
METHODS FOR CLOSE AUTOMATIC CONTROL OF 
INCUBATING TEMPERATURES IN 
LABORATORIES. 
By John T. Bowen, Technologist, Dairy Division. 
CONTENTS. 
Page. 
Construction of temperature-control 
compartment 2 
Construction of room 2 
Heating equipment 5 
Page. 
Description of temperature-control 
systems 7 
Temperature recorders 11 
Cost of operation I6 
The automatic control of temperature within close limits is very 
important in many lines of commercial work. It is of special im- 
portance, in fact, is a necessity, in laboratories where chemical, bac- 
teriological, and physiological investigations are conducted. In 
many instances success in the maintenance of cultures depends upon 
th?. ability continuously to maintain practically constant temperature. 
Pathogenic microorganisms, as a. rule, do not grow except Avithin very 
narrow temperature limits, the optimum temperature being about 
37.5° C. (99.5° F.). 
The Bureau of Animal Industry, United States Department of 
Agriculture, produces tuberculin on a large scale ; about 16,000 culture 
flasks of 300 c. c. capacity are maintained to produce the required 
quantity. The tubercle bacillus is very sensitive to temperature 
changes. In order to obtain the best growths, therefore, the tempera- 
ture during the period of incubation should be maintained practically 
constant at the optimum of about 37.5° C. To hold the temperature 
in all parts of the chamber approximately constant requires con- 
siderable care, especially if the chamber is large. 
Other work carried on by the bureau includes the study, by 
bacteriological means, of other diseases of domestic animals. The 
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