i6o 



Journal of Agricultural Research 



Vol. VI, No. 4 



From Table II it is seen that very few of the forms are killed in 30 

 seconds at 145° F. (62.8° C); nearly all, however, are destroyed at 155° 

 F. (68.3° C). None of the colonies found at 165° F. (73.9° C.) and 

 175° F. (79.5° C.) were produced in both tubes. The chance of error 

 is not fully eliminated in these cases. The consistent character of the 

 whole table and the innocuous character of the few organisms in which 

 occasional colonies occurred after heating show that temperatures of 

 165° to 175° F. (73.9° to 79.5° C.) for 30 seconds do practically destroy 

 the spores of these molds as they may be found in milk, although a few 



conidia in some species may occa- 

 sionally survive. 



Figure 2 shows graphically the 

 effect of the flash process of pasteur- 

 ization on mold spores. 



DESTRUCTION OF MOLD SPORES 

 BY DRY HEAT 



The third series of experiments 

 was planned to find the relative 

 ability of the spores of approxi- 

 mately the same organisms to endure 

 heating in dry air for the same 

 period as used for heating in milk. 

 After some experimentation the fol- 

 lowing method was used: Strips of 

 heavy filter paper were cut wide enough so that only the edges would come 

 into contact with the glass when dropped into test tubes. A drop of sterile 

 water carrying a suspension of the spores under experiment was depos- 

 ited in the middle of the paper strip and allowed to evaporate overnight. 

 The tubes were then immersed in liquid heated to the desired tempera- 

 ture and held 30 minutes after check tubes carrpng thermometers indi- 

 cated that the air in the tubes had reached the same degree. The tubes 

 were then removed and cooled. Melted agar was allowed to run into 

 each tube to form a slant and the cultures were set away at room tem- 

 perature. Observations of growth were made as in the previous experi- 

 ments and the results tabulated in the same manner in Table III. 





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Fig. 2. — Curve of the number of species of molds 

 surviving flash pasteurization at a series of 

 temperatures. 



