154 INFLUENCE OF PHYSICAL AGENTS. 
In considering the influence of high temperatures we must take 
account of the very great difference in the resisting power of the 
vegetative cells and the reproductive elements known as spores, also 
of the fact as to whether dry or moist heat is used and the time of 
exposure. 
Dry Heat.—When microérganisms in a desiccated condition are 
exposed to the action of heated dry air, the temperature required for 
their destruction is much above that required when they are in a 
moist condition or when they are exposed to the action of hot water 
or steam. This was thoroughly demonstrated by the experiments of 
Koch and Wolffhiigel (1881), A large number of pathogenic and 
non-pathogenic species were tested, with the following general result : 
A temperature of 78° to 123° C. maintained for an hour and a half 
(over 100° for an hour) failed to kill various non-pathogenic bacteria, 
but was fatal to the bacillus of mouse septiceemia and that of rabbit 
septicemia. To insure the destruction of all the species tested, in 
the absence of spores, a temperature of 120° to 128° C., maintained 
for an hour and a half, was required. 
The spores of Bacillus anthracis and of Bacillus subtilis resisted 
this temperature and required to insure their destruction a tempera- 
ture of 140° C. maintained for three hours. This temperature was 
found to injure most objects requiring disinfection, such as clothing 
and bedding. But the lower temperature which destroys micro- 
érganisms in the absence of spores (120° C. = 248° F.) can be used 
for disinfecting articles soiled with the discharges of patients with 
cholera, typhoid fever, or diphtheria, as the specific germs of these 
diseases do not form spores. It is probable also that it may be safely 
used to disinfect the clothing of small-pox patients, for we have ex- 
perimental evidence that a lower temperature destroys the virulence 
of vaccine virus (90°-95° C.—Baxter). 
In practical disinfection by means of dry heat it will be necessary 
to remember that it has but little penetrating power. In the experi- 
ments of Koch and Wolffhiigel it was found that registering ther- 
mometers placed in the interior of folded blankets and packages of 
various kinds did not show a temperature capable of killing bacteria 
after three hours’ exposure in a hot-air oven at 133° C. and above. 
Moist Heat.—The thermal death-point of bacteria, in the ab- 
sence of spores, is comparatively low when they are exposed to moist 
heat. The results of the writer’s experiments are given below: 
“In my temperature experiments I have taken great pains to insure the 
exposure of the test organisms to a uniform temperature, and have adopted 
ten minutes as the standard time of exposure. The method employed 
throughout has been as follows: From glass tubing having a diameter of 
about three-sixteenths of an inch I draw out in the flame of a Bunsen burner 
a number of capillary tubes, with an expanded extremity which serves as 
