IOI2 The American Naturalist. [ November, 
A further experiment showed that if the milk used be stert/ized before 
it is treated with oxygen and ozone, and is then proren Son con- 
tact with unfiltered air, no coagulation occurs, no matte much 
oxygen is introduced. We have subjected sterilized milk to po action 
of the electric spark for over an hour, and then kept this milk in our 
laboratory two months, without the appearance of the least sign of 
coagulation. 
From the fact that only a slight hastening of the time of souring 
resulted in the case of ordinary milk, and that no coagulation at » 
all was produced if the milk were sterilized, we conclude that the 
process cannot be one of oxidation, but is due rather to the rapid 
growth of the bacteria of the milk under the influence of the free 
oxygen, and, possibly, to a certain extent, of the ozone also. 
It is possible that during a thunder storm a sufficient amount of 
ozone may be generated to stimulate the bacteria and bring on a rapid 
souring. It seems very improbable, however, that the small amount 
of ozone usually produced at such a time could have any such effect. 
The true cause, it seems to us, is'to be found in the warm, sultry 
atmosphere which usually precedes and accompanies these storms. 
These atmospheric conditions, as is well known, are especially favora- 
ble to the growth of bacteria, and this rapid growth brings on a cor- 
respondingly rapid souring of the milk. 
These are, in brief, the conclusions at which we have arrived from 
the results of our experiments. They are, to a certain extent, borne 
out by the experience of the proprietor of a neighboring creamery. He 
finds that if milk be kept at a uniformly low temperature, no trouble 
` results from souring during the thunder-storm season. 
It will be seen from the above that ozone, at least in the small 
amount (about five per cent.) which can be generated from a given 
amount of oxygen by the electric spark, is not destructive to the 
bacteria which causes the souring of milk. This fact is of ifiterest, in 
view of the common use of ozone as a disinfectant.—AAaRon L. 
TREADWELL, Biological Laboratory, Wesleyan University. 
The Parry Herbarium.—This important collection of plants 
has been carefully arranged and catalogued, and is now offered for sale 
by Mrs. E. R. Parry, the widow of Dr. Parry. It is particularly 
rich in western and southwestern species. The whole number of 
determined specimens is eighteen thousand, representing 6,780 species- 
By far the greater portion of the species are North American, but 
seven hundred being natives of other parts of the world. Itis tobe 





