THE THEORIES OF IMMUNITY. 
121 
of these cultures were rendered immune. The blood serum, of 
such animals was also found to be capable of producing im¬ 
munity in other animals. The same was also found to be true 
with a few other pathogenic germs. This experiment led to 
the present anti-toxine treatment for diphtheria. To this gland 
may be attributed the certain degree of immunity enjoyed by 
certain young. 
It is worthy of note that by far the majority of pathogenic 
bacteria are only capable of producing disease by the products, 
toxalbumins, of their multiplication within the system, or by 
the absorption of these products through the tissues, as in diph¬ 
theria and tetanus, and, that the immunitive substance in the 
blood or tissue must have the power of neutralizing these toxal¬ 
bumins. In support of this theory Arloing has been able to 
produce symptomatic anthrax in naturally immune animals by 
adding certain chemicals to the cultures with which they were 
inoculated ; thus seeming to indicate that the immunitive sub¬ 
stance was destroyed by the chemical. 
The subject of acquired immunity deserves our special atten¬ 
tion ; since the whole army of bacteriologists seems to be cen¬ 
tred upon that one point for distinction, and, while as yet but 
little is known on the subject, marvelous revelations may be 
looked for in the comparatively near future. 
It is a well established fact that a single attack of such 
diseases as small-pox, scarlet fever and yellow fever generally 
confer immunity from subsequent attacks. It is interesting to 
note, too, that this immunity is a duration of a life-time. In 
the above mentioned diseases the system becomes affected in 
general, although this is not necessary to produce perfect im¬ 
munity ; for we have similar results from such local affections 
as whooping-cough and mumps. In the first instance the im¬ 
munitive substance is developed within the system, while in the 
second it must be absorbed from the infected area. It is also 
worthy of note that an attack of a certain infectious disease does 
not render the patient immune from other infectious diseases. 
A number of theories have been advanced as to the nature 
