, particularly his finger nails,
with soap and water and then bathes them in a solution of bichloride of
mercury before touching the patient in any place where infection might
occur. The difficulty, even with this great care, of freeing their hands
from bacteria has been found to be so great that, in late years,
surgeons have preferred to use, during operations, thin rubber gloves
which can be boiled before using and can be soaked in a stronger
antiseptic than the hands could bear.

It is extraordinary, from the standpoint of self-infection, to see how
men can be so careless as to sit down to dinner, after having worked in
places where their hands have come in contact with all sorts of organic
filth, without stopping to wash those hands even in cold water. It is
certainly providential that disease germs are as uncommon as they are,
for with the careless habits of most people in putting their hands to
their mouths, the death-rate from infectious diseases would be much
higher than it is except for the fact that most of the germs thus
introduced into the mouth are not disease-producing.

_Disinfecting by heat._

Better than any chemical agent known to be a destroyer of bacteria is
heat in one form or another. This may be steam or hot water or dry heat.
If a high enough temperature is maintained for a sufficient length of
time, the action is absolutely destructive to all germs. Fire does, of
course, destroy bacteria along with whatever material the bacteria are
concealed in, but such a disinfectant is of little value for ordinary
purposes, since the object of disinfection is to destroy bacteria
without destroying the surface on which they are lodged. In some old
buildings, where consumption or smallpox, for example, has become
permanent, it may be that the surest way of killing all the bacteria is
to burn up the house.

_Dry heat._

Unfortunately, even a moderate heat cannot always be applied. One's
hands, for example, can neither be heated in an oven to the necessary
temperature for destroying bacteria in their pores, nor can they be
immersed in boiling water or steam for a sufficient time to secure
thorough disinfection. Therefore, with the body, chemical means for
disinfection must be employed. Also when it is desired to disinfect a
liquid, such as beef broth, in which the experimenter desires to grow
some particular species to the exclusion of all others, dry heat is
inapplicable because it would evaporate the liq