THE NATURE OF THE ANAPHYLACTIC REACTION 137 
Ordinarily, iinmunolopeal processes are elicited by repeated paren- 
teral administrations of the antigen at intervals of a week or less. 
Repeated administrations of antiijen at freqnent intervals (less than a 
week apart) induce a condition of j,n'adually increasinj^; tolerance to the 
antigen, which is spoken of as immunity. The ana])hylactic process 
differs mechanically from an inununological process in that a single 
parenteral administration of antigen is made; this single injection of 
antigen leads to a condition of hypersusceptibility or susceptibility to 
the antigen. After an interval of eight to ten days as a minimum, a 
reinjection of the homologous protein, or anaphylactogen, elicits the 
anaphylactic reaction. 
The specific antibody, or anaphylactin, circulates in the body fluids 
in a reactive state when sensitization is complete, and it may persist 
in a reactive state for a very considerable period thereafter. It is 
important to realize, how^ever, that the anaphylactic reaction itself 
occurs within certain cells of the body and especially in association 
with tissues rich in smooth muscle. The symptomatology elicited 
varies somewhat in accord with the distribution of smooth muscle in 
various animals. Thus, in guinea-pigs the bronchi, which are relatively 
rich in smooth muscle, contract, causing acute respiratory embarrass- 
ment. In the dog, there is marked engorgement of the liver and the 
splanchnic circulation, causing a fall in general systemic blood-pressure. ^ 
There are circulatory disturbances, marked distention of the right 
heart, and fall in arterial blood-pressure in the rabbit. In all sus- 
ceptible animals there seems to be increased capillary permeability. 
Rosenau and Anderson- found that guinea-pigs may remain sensitized 
for more than two years. 
The injection of the serum of an animal containing anaphylactin 
will induce a condition of sensitiveness to the anaphylactogen in a 
normal animal of the same species after a brief latent period, usually 
less than twenty-four hours. When this latent period has passed, 
the injection of the homologous protein induces the characteristic 
anaphylactic reaction with symptoms quite as typical as those elicited 
in the originally sensitized animal. This condition of induced ana- 
phylaxis in a normal animal by parenteral administration of the serum 
from a sensitized animal is spoken of as a passive anaphylaxis. A 
state of passive anaphylaxis may be transmitted through a sensitized 
mother to the offspring. Guinea-pigs also may be passively sensi- 
tized by injecting a small amount (0.1 to 0.5 cc.) of blood from a rabbit 
that has been highly immunized to a specific protein as egg-white, and 
whose serum shows a high precipitin titer. Thus, the offspring of 
sensitized guinea-pigs were found by Rosenau and Anderson to be 
sensitized, and they also would therefore, react to an injection of the 
anaphylactogen in a characteristic manner. 
The specificity of the anaphylactic reaction is comparable to that 
1 See Simonds: Jour. Am. Med. Assn., 1919, 73, 1437. 
2 Bulletin No. 50, 1909, U. S. Public Health and Marine-Hospital Service. 
