2 BULLETIN 240, U. S. DEPARTMENT OF AGRICULTURE. 
It is evident from the report of Gerber and Wieske (2) that pas- 
teurization in bottles has been practiced in certain localities for a 
considerable period of time. According to these authors, pasteuri- 
zation in bottles by the process of Gerber, which consists of heating 
milk in bottles for one hour at 65° C. (149° F.), during which they 
are agitated, had been practiced in certain dairies for 15 years pre- 
vious to 1903. 
In this country milk has been pasteurized directly in bottles at 
various Strauss infant milk stations for several years, but this proc- 
ess has not been used on an extensive commercial scale until within 
the last two years. During the summer of 1910 an investigation was 
started of the bacteria which survived pasteurization in flasks and 
of the efficiency of the process. A report of this work has been pub- 
lished in Bulletin 161 of the Bureau of Animal Industry (3). 
While this work was in progress North (4) suggested the pasteuri- 
zation of milk in bottles on a commercial scale by the use of machines 
similar to those which have been in use in breweries for several years. 
The process of pasteurizing in bottles consists in bottling the milk 
in specially constructed bottles of sufficient size to allow a space in 
the top of the bottle to take care of the expansion of the milk during 
heating. The bottles are capped with special water-tight caps and 
submerged in hct water. After the milk in the bottles has reached 
the pasteurizing temperature, the temperature is maintained for 30 
minutes ; the hot water is then replaced by cold and the milk cooled. 
In general it takes about 30 minutes to heat the bottles, 30 minutes 
for the holding period, and 30 minutes to cool. Milk is also pas- 
teurized in the bottle by heating and cooling with water which is 
sprayed over the bottles. By this method of spraying, ordinary 
caps with a protective covering can be used; this will be described 
in another place in this bulletin. 
This process of pasteurizing in bottles is now used on a commer- 
cial scale in a number of milk plants throughout this country. 
Numerous advantages of this method of pasteurization over the 
ordinary methods have been claimed particularly in relation to the 
far superior bacterial reductions obtained. The most obvious point 
of advantage of this process is the prevention of reinfection after 
pasteurizing, but it seems as though a modification of the present 
system of "holder" pasteurization by bottling the pasteurized milk 
while hot, as suggested previously by the senior writer (5), would 
help to solve the problem of reinfection. 
Accordingly, the general object of the work hereinafter described 
has been to compare on a laboratory scale pasteurization in bottles 
with the process of bottling hot pasteurized milk. The special ob- 
jects have been to determine the bacterial reductions in each process, 
to study any special points which must be considered in the opera- 
