STERILIZATION. 47 
sterilized by steaming twenty to thirty minutes on three consecutive days, but will 
develop bacterial growths when put into the thermostat. If such were really the 
case, milk would be one of the worst of culture-media instead of one of the best. 
The general experience of bacteriologists is not in accord with this statement. 
Occasionally, in my own experience, a single steaming of five or ten minutes has 
sufficed to sterilize milk 
completely, at least so far as 
relates to organisms which 
grow aerobically and at tem- 
peratures under4o°C. Such 
milks have remained un- 
changed for two or three 
months at room tempera- 
tures (20° to 25° C.), and 
also in the thermostat at 
blood heat. For anaerobes, 
or organisms which will 
grow only at temperatures 
above 40° C., I have not 
tested. 
One possible source ot 
error in the use of steam 
for sterilization is ignorance 
of the exact temperature of 
the steam-chamber. Every 
steam-sterilizer should have 
a hole punched through the 
top, into which is fitted a 
cork through which a ther- 
mometer projects into the 
chamber. In this way may 
be determined beyond doubt 
for just how many minutes 
the media has been exposed 
to steam at 100° C. The 
Arnold _ steam - sterilizer, 
which is one of the best, 
is greatly improved by this 
simple device (fig. 42 and 
pl. 6). In this sterilizer there is a double bottom under the water-pan. The lower 
bottom is in contact with the Bunsen flame. ‘Through small holes in the upper 
Fig 43.* 
*Fic, 43—Improved Lautenschlager centrifuge. Capacity, 540 cc. Revolutions per minute, 
3,000 to 4,000. It requires about 3 horsepower to run the apparatus at this high speed, About one- 
eleventh natural size. Pe ’ 
+This remark does not apply to the Arnold combination steamer and dry oven, which can not 
be recommended. 
