158 



Journal of Agricultural Research 



Vol. VI, No. 4 



ing with 2 to 4 inches of capillary tube approximately 0.5 mm. in diame- 

 ter. The open end of each tube was plugged with cotton. The tubes were 

 packed into a copper case and dry-sterilized. F'or each experiment a few 

 drops of sterile milk were transferred to the conidial surface of a colony 

 and the conidia stirred into the milk. A column of milk 15 to 30 mm. 

 long, bearing numerous conidia, was then drawn into the capillary tube 

 and the end sealed in the flame. Experiments had shown that alcohol 

 boiling at 172.4° F. (78° C.) when so treated would boil in 20 to 30 sec- 

 onds when the tubes were thrust into water at 1 74.4° F. (79. i ° C.) . This 

 showed that milk containing mold spores could be heated in from 20 to 

 30 seconds in capillary tubes to any given temperature when immersed 

 in water 2 degrees Fahrenheit above the desired pasteurizing temperature. 

 In our experiments, therefore, it was possible to duplicate flash pasteuri- 

 zation on a laboratory scale; for example, to pasteurize at 165° F. 

 (73.9O C.) the capillary tubes containing milk and mold spores were held 

 in water at 167° F. (75° C.) for i minute. During this period about 30 

 seconds were required to heat the milk and it was held at the pasteurizing 

 temperature the other half minute. This is approximately the heating 

 period of milk in commercial flash pasteurization. After heating for the 

 required time, the tubes were cooled by thrusting them into cold water. 

 The tip of the capillary was then broken off and the contents streaked 

 upon slanted Czapek's solution agar. The slants were incubated, observed 

 occasionally, and the results of the various experiments were tabulated 

 separately and then brought together in Table II. 



Tabi.E II. — Comparative effect of heating mold spores in milk to temperatures of from 

 145° to 175° F. {62.8° to 79.5° C.)for JO seconds 1 



1 I.O, a typical colony; decimals, proportionate growth; o.o. no growth; ?. inharmonious results. 



