57 
when the interval between the first and second injection is over 
four months they obtained little or no immediate reaction, but what 
they termed “an accelerated reaction/’ for the fever, urticaria, and 
other symptoms of the serum disease appeared on the fifth, sixth, 
seventh, or eighth day. It will be remembered that the normal 
period of incubation for the symptoms of the serum disease to appear 
after the first injection is between the eighth and thirteenth day. 
Von Pirquet and Schick lay special stress upon the phenomena of 
the “immediate” and “accelerated” reactions following the second 
injection. 
We might also conclude despite the suggestion contained in Part 
X of our work upon sensitizing guinea pigs by feeding them with 
horse serum or horse meat that children may not be sensitized to 
the toxic action in horse serum by eating horse meat from the fact 
that horse meat is a favorite article of diet in certain European 
countries, and there is nothing on record to show that the injection 
of horse serum in those countries is fraught with more danger than 
where this practice does not obtain. We must, however, remember 
that our work has shown that guinea pigs are sensitized with exceed- 
ingly minute quantities of the strange proteid, and that repeated 
injections cause an immunity; and it is possible that the same 
action may be true of feeding. 
Man reacts to the first injection of horse serum after a period of 
incubation of eight to thirteen days. Guinea pigs show practically 
no reaction following the first injection. Both react to a second 
injection. The reactions in man and the guinea pig, however, differ 
both in severity and kind. The relation, therefore, that our obser- 
vations upon the guinea pig may have in its application to man 
must await further study. Of course, the fact that other animals 
besides man and guinea pigs react to a second injection of horse 
serum would seem to indicate that we are dealing with one and the 
same action. 
We have tested monkeys, rabbits, mice, dogs, cats, rats chickens, 
and pigeons to determine whether any of these animals may be sen- 
sitized to the action of horse serum. Thus far we have obtained a 
response in the dogs, rabbits, and cats. This work is still in progress 
and will be reported at a future date. 
Yon Pirquet and Schick also found that the first injection into 
rabbits caused no clinical effect, but that subsequent subcutaneous 
injections caused immediate reaction in the production of local edema 
which extended even to gangrene. Second injections, when intro- 
duced intravenously, produced symptoms of collapse and even 
death. 
