NATURAL RESISTANCE TO DISEASE—FLEXNER. 7385 
settled question whether they are altered qualitatively by the immuni- 
zation, or whether the plasmatic changes do not really react upon 
them and thus increase their efficiency. 
It must now be patent that between what may be termed the proc- 
ess of physiological resistance and what is termed the condition 
of immunization, a wide distinction exists. The one is nonspecific 
in its action, the other highly specific in its effects; the one is sub- 
ject to a limited augmentation, the other may be carried to a high 
degree of potency and perfection; the one often fails to protect 
the organism in which it is developed, the other suffices to protect 
both itself and another organism. If therefore we were to be asked 
in what manner can the animal organism best be reenforced against 
infection, we should be compelled to answer by passing safely through 
the infection itself. This conclusion, which has been reached by 
purely experimental biological methods, is supported on every side 
by common observation and experience with the acute infectious 
diseases of which one attack protects from a subsequent attack of 
the same disease. 
It may conduce to clearness if we should enumerate the factors that 
have been described and assigned on the one hand to natural resist- 
ance, and on the other hand to acquired resistance or immunity. We 
ean tabulate the factors in the following manner: 
NATURAL OR PHYSIOLOGICAL INCREASED NATURAL OR PHYSIOLOGICAL 
RESISTANCE, RESISTANCE. 
complement. complement, probably increased. 
; intermediary body. ; intermediary body. 
Alexin f y y Alexin i y y 
opsonin. opsonin. 
agglutinin. agglutinin. 
Phagocyte. Phagocyte—increased (hyperleucocytosis). 
ACQUIRED IMMUNITY. 
Complement—probably increased. 
Intermediary body—specifie one produced. 
Opsonin—specific, stabile one produced. 
Agglutinin—specifie one produced. 
for exotoxin 
for endotoxin 
Phagocyte—often increased but qualitatively unchanged. 
Antitoxin produced. 
This tabulation exhibits the distinction between the physical basis 
of physiological resistance and of the state of immunity. There is 
another difference between them; any increase that can be called out 
beyond the mean of physiological resistance is accomplished in a few 
hours; and having been called out to meet a particular condition of 
need of the body and the effect having been exerted, it passes off very 
soon. It is rare that the effect of a hyperleucocytosis can be detected 
