Frost—Bacteriological Control of Public Milk Supplies. 1311 
It would thus seem that the effectiveness of different auto¬ 
claves varies when run in htis manner and that considerable 
work would have to be done with a particular autoclave to de¬ 
termine whether or not a single exposure is effective and, if so, 
the time and pressure required. It seems certain, however, that 
two exposures on consecutive days would always be effective, es¬ 
pecially if the bottles were put in the incubator between heat- 
tings. Whatever the method of sterilization employed, it seems 
desirable to use bouillon or peptone water instead of the water 
in these “water blanks,” especially if they are to be carried 
about in portable outfits, in order that the danger from contami¬ 
nation by growth in them may be readily detected. 
VI. Loss Due to Evaporation on Standing. 
It is a matter of considerable convenience, especially in the 
smaller laboratories, to sterilize a number of these “ water 
blanks” at once and store them ready for use at any time. If 
this is done it is important to know the rapidity with which 
evaporation will take place on standing. The rate will depend 
upon a number of factors, such as the size and shape of the 
bottle, the size of the mouth, the temperature of the room and 
the humidity of the air. Tn regard to the size of the bottle, it 
is probably only necessary to consider the area of the exposed 
surface compared with the volume of the fluid. On this account 
a tall narrow bottle is better than a broad one. Likewise, it is 
apparent that a narrow bottle is more desirable than a wide¬ 
mouthed bottle. The amount of evaporation from one hundred 
cubic centimeters in an ordinary eight-ounce narrow-mouthed 
Blake bottle is shown in the following table: 
Table d. 
Loss due to Evaporation. 
Number of 
Loss due to 
Time of 
Loss due to 
Total loss. 
bottles. 
sterilization. 
standing-. 
standing-. 
10 
4.1 grams 
8 weeks 
8 
4.9 grams 
4.8 
9% 
Without caps 
10 
4.3 
9.1% 
With caps 
This evaporation might be prevented by the use of glass stop¬ 
pered bottles. Such, however, are not satisfactory for other 
reasons. The same end can be attained by the use of cotton 
