24 PRACTICAL DAIRY BACTERIOLOGY 



but the result demonstrated beyond a doubt that the* electric 

 current will not sour milk. It was then suggested that the 

 electricity of the thunder storm produced ozone in the air, and this 

 hastened the souring. This ozone theory, also, was carefully 

 tested and proved to be without foundation, for ozone in itself 

 has no power of affecting milk. Moreover, further experiments 

 proved that, unless bacteria are in the milk, thunder storms 

 have no effect. Milk that is deprived of bacteria may be kept 

 for months during the whole season of thunder storms and 

 never show the slightest trace of souring, showing, of course, 

 that thunder storms have no direct action upon the milk, since 

 they never affect milk from which the bacteria have been re- 

 moved. Practical experience has also shown that if the milk is 

 kept sufficiently cold in an ice chest, or by other means, the 

 thunder storms have no effect upon it. Only milk that is not 

 sufficiently cooled, or that is not cooled at all, is affected by 

 thunder storms. From all these facts it becomes evident that 

 if thunder storms have any effect upon milk it is only indirect. 

 The reason that the souring of milk frequently occurs at 

 the same time with thunder storms seems to be very simple. 

 Bacteria will grow most readily at warm temperatures. Thun- 

 der storms occur at seasons of the year when the tempera- 

 ture is high; and the same atmospheric conditions which bring 

 on thunder storms are likely, and, indeed, certain, to stimulate 

 the growth of bacteria. If the temperature is high, and the 

 milk is not sufficiently cool, it will sour very rapidly, whether 

 any thunder storms are occurring or not. Hence it is not 

 strange that, after a thunder storm, we often find milk which 

 has not been kept cool, soured and curdled, and our natural 

 inference is that the thunder storm has had some connec- 

 tion with it. The whole phenomenon appears to be one of 

 bacteria growth, stimulated by warm temperature. The souring 

 of milk by thunder storms may be absolutely prevented by 

 keeping the milk cool. 



