508 IMMUNITY AND PROTECTIVE INOCULATION 
These groups have the greater variety of function, especially those of nutrition and 
assimilation. This theory teaches that immunity depends upon the presence or 
absence of certain substances which he calls receptors or lateral chains which certain of 
the cells possess. These receptors are concerned in the normal nutrition of the cells 
and have affinities for various complex albuminous substances. Among these sub- 
stances are the molecules of the toxin produced by certain bacteria and possibly other 
poisons. Every toxin has affinities described as haptophorus and toxophorus, that is, 
each molecule of the toxin is composed of two different groups of atoms, the one the 
toxophore or poisonous group, the other the haptophore or combining group of atoms. 
The haptophorus atoms of the toxin molecule combine or unite with the receptors of 
those cells for which they have special affinity and through the haptophore group the 
toxophore part of the molecule is able to act upon the cell. In some cases the cells are 
destroyed and in others additional receptors are produced because of the stimulation. 
These receptors may pass out of the cell into the serum, where they act as free receptors 
or immune bodies to lock up or neutralize the toxin. The free receptors are the active 
part of the antitoxin. 
Ehrlich illustrated his theory by the use of diagrammatic figures to represent the cell 
throwing off “receptors,” the receptors or antitoxin locking up or neutralizing the toxin 
and the effect of the anti-bodies on the toxin and its complement. 
The protein sensitization or proteolytic ferment theory has been advocated by Vaughn 
an explanation of immunity. In brief, the theory as stated by Vaughn is this: ‘‘Pro- 
tein sensitization consists in developing in the animal body a specific proteolytic fer- 
ment which digests the same protein on reinjection.”” Like the other theories, this one 
must be proven by the crucial test of experimental work. 
Still more recently another theory to explain immunity has been advanced by 
Williams and Beveridge and called by them the “‘Proteomorphic theory.” 
Hemolysins. Belfanti and Carbone, in 1898, pointed out the fact 
that if horses were injected with the red blood cells of rabbits the 
serum of these horses would be more or less toxic for rabbits. This 
result was followed by some interesting experiments by Bordet in 
which he showed that the blood serum of guinea pigs which had been 
injected several times with from three to five cubic centimeters of 
defibrinated rabbit’s blood acquires the property of rapidly dissolv- 
ing in a test tube the red blood cells of a normal rabbit’s blood. The 
serum of an untreated healthy guinea pig will not do this. It was 
pointed out that this reaction was specific, that is, the serum of ani- 
mals treated with rabbit’s blood (specific serum) dissolves the red 
corpuscles of the rabbit’s blood only. This property that had been 
demonstrated in the blood serum of guinea pigs treated with rabbit’s 
blood was shown to hold for the sera of other species of animals treated 
with the blood cells of a different species. Wassermann has formu- 
lated this action as follows: ‘““The serum of animals species A, after 
these have been injected either subcutaneously, intraperitoneally, or 
intravenously with erythrocytes of species B, acquires an increased 
