2S4 
CHARLES H. HIGGINS. 
that the causative organism could be cultivated in a specially 
prepared chicken broth. Returning to his laboratory after an 
absence of a few days, he observed that cultures made prior to 
|his departure no longer produced the disease in susceptible 
fowl. Securing a fresh organism from another outbreak, he 
found that the fowls previously inoculated did not contract the 
disease, although susceptible fowl not so inoculated became af¬ 
fected and died in the usual period. He was thus able to demon¬ 
strate, largely by accident, that cultures of the bacteria respon¬ 
sible for the ravages caused by this disease could be atten¬ 
uated and that such attenuated cultures were capable of es¬ 
tablishing resistance or immunity in susceptible animals when 
used in suitable doses. Applying this knowledge to anthrax, 
he was able, in 1881, to prepare an attenuated virus which 
conferred immunity against this affection. Anthrax vaccine 
is now a commonly used biological product, although there 
is danger, and serious losses have been reported following the 
use of an improperly prepared or impotent product. In con¬ 
nection with these attenuated vira it is of interest to note that 
investigators have shown that the inoculation with an organism 
usually harmless, may be capable of conferring a passive im¬ 
munity against a disease. For example, the Bacillus pyocyaneus 
confers immunity in sheep against anthrax for a limited period. 
From this groundwork on immunity and the constant increase 
in our bacteriological knowledge we have witnessed the intro¬ 
duction and extensive use of bacterial filtrates. Some of these 
such as tuberculin, introduced by Koch, and mallein, introduced 
by Von Preusse and Kalning, are well known diagnostic agents 
and are often improperly called toxines. With the preparation 
of the bacterial filtrates just mentioned, which we now know to 
be thermo-stable, further experiments indicated the development 
of true toxines such as diphtheria and tetanus which are not 
thermo-stable. The unheated sterile filtrates from these latter 
organisms were found to be fatal in extremely minute quanti¬ 
ties when injected beneath the skin of suitable experimental 
animals. With the knowledge .that recovery from an attack of 
