DOT 
the abdominal cavity of an animal, when the bacteria which were tested 
were previously treated with normal serum of another animal, Pfeiffer 
and Friedberger had already previously shown.’ In their most recent 
article they emphasize that this phenomenon can not be explained upon 
the aggressin hypothesis of Bail. They also show that it can not be 
elucidated upon the assumption that, when the normal serum is added 
to the bacteria, soluble substances, the free receptors of the organism, are 
taken up by the serum; and moreover that its action does not coincide 
with the theory of Sachs of complement deviation, which was suggested 
for the explanation of what at first appeared to be a similar process 
observed in haemolysis. 
Pfeiffer and Freidberger on the contrary believe that this antagonistic 
action represents the fundamental properties of a normal serum, and the 
subject therefore is one of very great significance in the processes of 
immunity. While it must be added that all observers do not accept their 
explanation for this phenomenon, notably among them Gay,!! who believes 
that the explanation lies in the fact that specifie serum-precipitates 
which are able to fix alexine are present, nevertheless it seems entirely 
clear that the process can not be satisfactorily explained according to the 
aggressin theory of Bail. Wassermann and Citron’? in their paper have 
considered the question which is apparently of most practical importance 
in its relation to Bail’s studies, namely, whether in the infected organism, 
in the conflict between the invading bacteria and the cells of the host, a 
substance, aggressin, actually is formed, and whether this in reality is a 
new substance and one which, as yet, we have not been able to demonstrate 
in our investigations of the living bacteria outside of the body. 
As Wassermann has remarked, if this is the case then the further 
conclusions of Bail must be acknowledged, namely, that by means of 
aggressin an anti-aggressin serum can be obtained which will possess dif- 
ferent qualities from those sera previously obtained by other methods and 
which, perhaps, may act against the infection in a more favorable manner. 
Wassermann and Citron first performed experiments relating to this 
subject in exactly the same manner as Bail had recommended and found 
that they could confirm his work. They next investigated the question 
as to whether these substances, termed aggressins, were to be found only 
in the living organism as a result of the infection. Their experiments 
were performed with typhoid, hog-cholera, and swine-plague bacilli. 
Sterile exudates produced in rabbits by the injection of aleuronat were 
collected in glass vessels in an aseptic manner and their sterility proven. 
The living bacteria were then added to the exudates and were placed in 
an incubator at 37° for twenty-four hours. The mixtures were next 
centrifugalized and the clear fluid drawn off from above and sterilized. 
* Pfeiffer und Friedberger: Deutsche Medizin. Wehnschr. (1905), 31, 6. 
“Gay: Centralbl. fiir Bakteriol. Orig. (1905), 39, 603. 
* Wassermann und Citron: Deutsche Medizin. Wehnschr. (1905), 31, 1101. 
