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varying from to X qV o c. c. almost invariably render guinea pigs 
highly susceptible when given in the toxine-antitoxine mixture. 
One-tenth c. c. of horse serum injected into the peritoneal cavity 
of a susceptible guinea pig is sufficient to cause death. The same 
quantity inoculated subcutaneously may cause serious symptoms. 
There is some evidence to show that the sensitizing substance in 
horse serum is the same as the poisonous substance. The sensitiz- 
ing substance is not affected by precipitation with ammonium 
sulphate and dialysis. 
Guinea pigs may be sensitized with horse serum that has been 
dried and redissolved. 
The sensitizing substance is not affected by a temperature of 60° 
C. for 6 hours. 
It is probable that small quantities of horse serum render a guinea 
pig more susceptible than do large quantities. If this be true, it is 
due, perhaps, to the fact that large quantities, owing to slow absorp- 
tion or prolonged reaction, partly immunize the guinea pig at the 
same time that it is being sensitized. 
The sensitizing substance apparently is not free in the blood 
serum of guinea pigs. 
An active immunity against this toxic principle may readily be 
established by repeated injections of horse serum, at short intervals, 
into a guinea pig. Although guinea pigs may be immunized actively 
in this manner we have not yet succeeded in transferring this immu- 
nity in the blood serum or body juices to another guinea pig. It 
therefore appears that the immune bodies, if such exist against the 
toxic action of horse serum, are not free in the blood and body juices 
contrary to the case in diphtheria. 
Guinea pigs may be sensitized to the toxic action of horse serum 
by feeding them with horse serum or horse meat. 
The fact that guinea pigs may be rendered susceptible by the feed- 
ing of strange proteid matter opens an interesting question as to 
whether sensitive guinea pigs may also be poisoned by feeding with 
the same serum given after a proper interval of time. If man can 
be sensitized in a similar way by the eating of certain proteid sub- 
stances may not this throw light upon those interesting and obscure 
cases in which the eating of fish, sea food, and other articles of diet 
habitually cause sudden and sometimes serious symptoms? 
The susceptibility to the toxic action of horse serum is transmitted 
hereditarily from the mother guinea pig to her young. 
These results upon the hereditary transmission of the suscepti- 
bility to the poisonous action of horse serum in guinea pigs may 
throw light upon the well-known hereditary tendency to tuberculosis 
in children born of a tuberculous parent. There are certain anal- 
ogies between the action of tuberculosis and horse serum. Both 
