172 JOUENAL OF SCIENCE. 



This result was very constant. In a considerable number of 

 experiments, using milk of all degrees of sweetness, from that just 

 from the cow to that a day or more old, the same result followed, — a 

 slight hastening of the time of coagulation in milk treated with ozone 

 or oxygen. Between the time of coagulation of milk treated simply 

 with oxygen, and that treated with oxygen plus ozone, no perceptible 

 difference could be noticed. 



We had, then, in our experiments, produced a slight hastening 

 of the time of coagulation. Was this a direct oxidation ? From the 

 fact that it required over a day to act, it seemed likely that it could 

 not be. If, however, it were an oxidation, it ought to act as well on 

 sterilized milk — i.e, milk in which all bacteria have been killed by 

 heat — as on ordinary milk. We therefore, before introducing the 

 oxygen, sterilized the milk. In this case no coagulation occurred. 

 Milk that had been treated at two separate times, a week apart, with 

 oxygen and ozone, was kept for over two months without the 

 appearance of the least sign of coagulation. 



Briefly summed up, then, our results were as follows: — 



1. Milk, under the influence of oxygen, or oxygen and ozone, 

 coagulates somewhat earlier than when left in its normal condition. 



2. This action does not take place if the milk has been sterilized, 

 and is kept from contact with unfiltered air. 



3. It is probably, therefore, not an oxidation. The conclusion 

 drawn from this is that the souring was simply produced by an 

 unusually rapid growth of bacteria. The bacteria of milk are mostly 

 aerobic, and would undoubtedly be stimulated to rapid growth by free 

 oxygen or ozone. 



If in a thunderstorm ozone is set free, as some observers claim, 

 its action on bacteria would perhaps explain the effects produced at 

 such times. I am inclined to think, however, that a more probable 

 reason is to be found in the general conditions of the atmosphere 

 preceding and during the storm. It has been found in our laboratory 

 that bacteria growing on gelatine will multiply with unusual rapidity 

 during warm, sultry weather. Now, these are the atmospheric con- 

 ditions that usually precede and accompany thunder-storms. It 

 seems to me most likely, therefore, that whatever rapid souring occurs 

 is due to an unusually rapid growth of bacteria, caused by especially 

 favourable conditions of the atmosphere. 



The experience of the proprietor of a neighbouring creamery 

 confirms to a certain extent these conclusions. He finds, that, if milk 

 is kept at a uniformly low temperature during the thunder-storm 

 season, no trouble results from rapid souring, indicating that this 

 souring, when it occurs, is due more to a high temperature and sultry 

 atmosphere than to the ozone in the air. If this were a process of 

 direct oxidation, it should take place, partially at least, at the lower 

 temperature. 



Professor Tolomei finds, also, that a slight electric current, if 

 less than three amperes, will have a preservative effect on milk, the 

 current being passed directly through the liquid. A current greater 

 than three amperes will decompose the milk. 



