NOVEMBEE 26, 1915] 



SCIENCE 



771 



II. Tie influence of intermittent freezing and 

 thawing upon B. coU. 



If crystallization is in some way effective in 

 destroying germ life, then alternate freezing 

 and thawing should bring about a greater re- 

 duction than prolonged freezing. Table I. 

 shows a part of one of our protocols. It will 

 be noted that intermittent freezing has but 

 slightly greater germicidal value than has 

 sustained freezing for the same period of time. 



III. The effect of the degree of cold used in 

 the freezing mixture. 



Tubes containing the bacteria were frozen 

 and held for three hours for comparison at ap- 

 proximately — 15 degrees 0. and — 2 degrees 

 C. The colder temperature was considerably 

 more fatal. Tubes kept at + .5 degree C, 

 used as controls in most of the experiments, 

 showed marked variation, but seldom showed 

 over 30 per cent, to 40 per cent, of the bacteria 

 to be killed. 



rV. The composition of the media and its in- 

 fluence upon germ survival in freezing mix- 

 tures. 



It was with the object of studying this fea- 

 ture of the work that we began our experi- 

 ments. They are still very deficient, but what 

 we have found is worthy of consideration. 



Distille-d water and Boston tap water give 

 very uniform and comparable results. 



Using cream containing 30 per cent, of 

 butter fat, we found very striking protection 

 afforded the bacteria when frozen, whether the 

 freezing be continuous or intermittent. Held 

 at just above the freezing temperature, we find 

 about the same percentage reduction to occur 

 as in water, though the results are very erratic, 

 occasionally showing an increase during the 

 course of a few hours. Freezing and thawing 

 at intervals is considerably more fatal than 

 continuous freezing. A few typical results of 

 freezing B. coli in cream are given in the sec- 

 ond table. 



It is premature to suggest conclusions but 

 our results lead us to infer that the degree of 

 cold, time of freezing, crystallization and ex- 

 ternal pressure, and the composition of the 

 media in which the freezing occurs all have 



an influence upon the germicidal potency ex- 

 hibited by cold. Probably all of the explana- 

 tions for the mode of destruction, suggested 

 in the early part of these notes, must be con- 

 sidered as important. 



TABLE I 



A Comparison of the Percentage Seduction of B. 

 coli held at .5° C, — 15° C, and Frozen In- 

 termittently for a Three-hour Period 



TABLE II 



Percentage Seduction Obtained with B. coli in 

 Cream at Freezing Temperatures 



C. M. HiLLIAKD, 



Christina Toeossian, 

 EuTH P. Stone 



Simmons College 



SOCIETIFS AND ACADEMIES 



THE AMERICAN ASSOCIATION FOE THE ADVANCEMENT 

 OF SCIENCE SECTION OF EDUCATION 



The special summer session of Section L, Edu- 

 cation, of the American Association for the Ad- 

 vancement of Science met at the University of 

 California on Tuesday, August 3, and at Stan- 

 ford "University on the following day. The morn- 

 ing meeting on Tuesday was a joint meeting with 



