505 
form chemical substances in their protoplasm which so act upon the cells 
and fluids of the animal for which the organism is pathogenic that they 
overcome its natural resistance against the infection. This author at 
first designated these substances as lysines, but, owing to the fact that 
this term came to be employed in a different sense, he together with Bail 
more recently proposed for them the name of “aggressins.” 
Bail also points out that a bacillus must injure and overcome the ani- 
mal’s natural protective power in order to survive in the body of an 
animal and produce its particular disease. This it is able to do by means 
of its aggressive properties, which depend upon a certain substance which 
may be designated as “aggressin.” These aggressins he believes are only 
to be formed by the bacteria in the animal body and they are particularly 
to be encountered in pathological fluids such as cedemas and exudates 
which result from the inoculation of the different micro-organisms. 
Thus, anthrax aggressin is contained in the edematous fluid resulting 
from the subcutaneous injection into animals of the anthrax bacillus, 
whereas in the exudate which forms in the abdominal or pleural cavity 
of the rabbit or guinea pig, following the inoculation of the typhoid bacil- 
lus or cholera spirillum, typhoid or cholera aggressin is met with. He 
maintains that when these different exudates were carefully centrifugal- 
ized and thus freed from all the animal cells and most of the bacteria, and 
were then sterilized, in each instance a clear, yellow fluid resulted which 
contained the particular aggressin. For these substances he emphasizes 
the following distinctions: 
First. Non-lethal amounts of cholera and typhoid bacteria, when 
injected into the animal simultaneously with the corresponding aggres- 
sin, cause the death of the animal; that is, the aggressin stimulates the 
bacteria to the production of toxic substances in such quantities that the 
animal succumbs. 
Second. Fatal doses of these bacteria, which, however, give rise only 
to comparatively mild or subacute infections, produce with the aid of 
aggressin very severe and acutely fatal ones; hence the aggressin must 
aid the bacteria favorably in their struggle against the animal during the 
course of the infection. 
Third. By injections of aggressin into the abdominal cavity of animals, 
the protective action of a bactericidal serum may be suspended, 
Fourth. By the injection of aggressin an immunity is obtained which 
differs widely from bactericidal immunity. 
I believe Bail has by his extensive experiments undoubtedly demon- 
strated that results somewhat similar to those outlined in these conclusions 
occur for several infections, although it would appear that in typhoid fever 
and cholera his so-called aggressin immunity depends chiefly upon bac- 
teriolysis. However, as I shall point out further on, the results of all of 
his work with these substances are apparently in great part dependent 
upon the action of and explained according to entirely different processes 
