104 BACTERIOLOGY. 
with free circulation of blood and retention in the body 
of substances which should be eliminated also tend to 
lessen the vitality. In these and other similar ways 
animals which are otherwise refractory may acquire a 
susceptibility to disease. 
Immunization and Healing by Non-specific Means. Just 
as all conditions which are deleterious to the body lessen 
its power of resistance to bacterial invasion, so all con- 
ditions which are favorable to it increase its resistance, 
and thus aid in preventing and overcoming infection. 
The internal use of antiseptics against bacteria has 
not proved successful, for the reason that an amount 
too small to inhibit bacterial growth is found to be 
poisonous to the tissue cells. The efficacy of quinine 
in malaria and mercury in syphilis is, possibly, an ex- 
ception to the rule, but in both cases we are dealing 
probably with animal parasites, not ordinary bacteria. 
Such substances as nuclein and others contained in 
blood-serum, when introduced into the body in consider- 
able quantity, aid somewhat in inhibiting or preventing 
the growth of many bacteria. Even bouillon, salt 
solution, and small amounts of urine have a slight in- 
hibitory action. The hastening of elimination of the 
bacterial poisons by free intestinal evacuation and en- 
couragement of the functions of the skin and kidneys 
are also of some avail. The enzymes formed by certain 
bacteria have been found to exert a slight bactericidal 
action, not only on the germs which have directly or 
indirectly produced them in the body, but also on other 
varieties. None of these enzymes are sufficiently pro- 
tective to be of practical value nor equal in power to the 
protective substances formed by the tissues from the 
bacterial products. 
