( 622 ) 
sense. Since that time the guinea-pig has become the fit test-animal 
for such investigations. 
I have provisionally confined myself to the study of horse-serum, 
also because the knowledge of this in connection with the origin of 
our therapeutic sera has the most practical importance. 
While a normal guinea-pig bears an intraperitoneal or sub- 
cutaneous injection of 5cm’ horse-serum without any perceptible 
symptom of disease, such an animal (of 250 to 300 grammes) mostly 
perishes however under typical symptoms of intoxication, when about 
12 days before it has been treated with a small dose of the same serum 
fe.g +7/,,, Cm’). Instead of immunity (prophylaxis), which usually 
follows on the administration of a larger dose, here a state of hyper- 
susceptibility or anaphylaxis (Richet) has arisen. The borse-serum 
completely harmless in itself, plays in this case for the sensitized 
guinea-pig the part of a heavy poison. The first sensitizing injection 
must therefore have caused such changes in the organism as to 
change the second serum-injection into a toxic one. 
This process of reaction no doubt belongs to the symptoms of 
immunity, and consequently it ought to be studied with the aid of 
the methods that the doctrine of immunity has procured. It was 
therefore a matter of course that the question was asked: Is in the 
process in question alexine fixed? 
Orro') answers this question in the negative, in my opinion 
wrongly. For repeated observation taught me that a sensitized guinea- 
pig, which reacts upon the second serum-administration with symp- 
toms of intoxication some time after that injection produces a serum 
that is exceedingly poor in haemolytic alexine (sensitized red corpuscles 
serving as test-object). A short time (5—10 min.) after the toxic 
injection the alexie power of the pig-serum is still the same; after 
this it decreases gradually and rather rapidly, so that after '/,—1 
hour it has become minimum. In this period the animal mostly dies. 
If it recovers, however, the alexine is also seen to increase again, 
so that 1’/,—2 hours after the injection it has returned again to the 
normal level or even higher. This course of things might be graphi- 
cally represented by means of a curve. In a normal, not anaphylactic 
guinea-pig the alexine-quantity of the serum remains constant under 
the same experimental circumstances. 
Now, if the blood is not examined at the right moment, or not 
at several moments during the stage of intoxication, the chances are 
that one is too early (when the alexine has not yet disappeared) or 
1) Münch. med. Woch. 1907, no. 34. 
