A Theory of Ferments and Their Action. 
35 
mimes, and, therefore, feel that immunity formerly acquired has not 
been lost if vaccination fails to develop the characteristic pustule. This 
instance but represents a general rule which the term immunity itself 
implies. The reason why ferments and pathogens do not take when 
inoculated into immune persons is readily understood when the fact is 
recognized that, in accordance with the principle of interference, fer- 
ment and pathogen molecules can disrupt and recombine into specific 
antibodies only those substrates whose molecular waves coincide in 
certain definite ways with the ferments or pathogen, as the case may 
be, and since the related substrate (homologous proteid molecules of 
the blood serum) is destroyed or changed in molecular structure, be 
immunization, the related ferment or pathogen, as the case may be, 
is incapable of causing specific action in the blood of person immune 
to this substance. 
PHAGOCYTOSIS. 
Among the several kinds of Ieuc0c3d.es or white blood corpuscles, and 
some of the fixed tissue cells also, are to be found . cells whose chief 
function seems to be the removal of dead and foreign matters from the 
blood and tissues of the body. These cells are commonly known as 
phagocytes, and a theory of immunity, and a very popular theory, is 
based upon the claims that the phagocytes defend the body against in- 
fection by devouring, actually englobing and digesting, invading path- 
ogenic bacteria. I do not propose to discuss the phagocytic theory of 
immunity except to say, that the opposite behavior of phagocytes 
towards infectious bacteria in immune persons as against their behavior 
towards the same bacteria in non-immune persons, has presented a puzzle 
which those of the phagocytic school of immunity have failed to solve. 
I mention this phenomenon at this time because it confirms the accuracy 
of the contention, that the presence in the blood serum of a vulnerable 
substrate is absolutel} T essential to pathogenesis, and that the absence of 
either factor — pathogen or substrate — is fatal to the process. To illus- 
trate, it is an established fact that the phagocytes of a person who has 
been made immune to a given infectious disease will attract towards 
themselves, and will devour the specific bacteria of this disease which 
the blood may contain. On the other hand, when the same species of 
bacterium is inoculated into the body of a person who has not been 
made immune to this disease the phagocytes will not attack, but will 
he driven from the field and may be destroyed by the bacteria. In the 
first instance — according to the teaching of the biophysical theory — 
the pathogenic bacteria are innocuous to the immune person, and to his 
phagocytes as well, for the reason that during the process of his 
previous immunization certain homologous proteid molecules of Ids 
