64 MILK 
vestigations of Rentschler to kill quickly many 
forms of microbes, and may be applicable to the 
purification of milk, when, as in war, systematic 
protection and inspection are not possible. 
Preservation of Samples.—For the preservation 
of milk samples for a day or two, refrigeration 
is the best method. Sterilization in the ordinary 
steam sterilizer used in preparing culture-media, 
will enable milk to be kept for a considerable 
time if in a flask closed with a cotton plug. 
Several preservatives have been proposed for 
keepingsamples. Richmond found smallamounts 
of hydrofluoric acid effective, but it has been but 
little used. Formaldehyde is very efficient; in 
large amount it increases the total solids, inter- 
feres with the reactions of the proteins and simu- 
lates some of the reactions of the carbohydrates. 
A couple of drops of commercial formalin to 25 
c.c. will preserve a sample for several days. 
