15 
Fig. 1/.— Fourth stage; there, 
cep tors have left the cell and 
float free in the blood = anti- 
toxin. 
combining with the toxine are produced in many different parts ( f the 
body, especially in tissues and organs having the power of anchoring 
the toxine without causing serious poisonous effects. 
The connective tissue is believed to be especially rich in receptors, 
evidenced b}^ the lo(*al reaction caused by the subcutaneous inoculation 
of diphtheria toxine, ricin, abrin, and similar 
poisons. In fact, one would not be far wrong- 
in assigning a particular signiffcance, in the 
production of receptors, to just those organs 
which show unimportant vital response, because 
in such tissues the injurious effects of the toxo- 
phore group are absent or of such diminished 
importance that the regenerative powers of such 
tissues are not retarded. 
The presence or absence of receptors capable 
of binding the toxine, as well as their number 
and distribution, are factors which determine 
the susceptibility of different species of animals against the various 
toxines. These factors also determine the individual variations in the 
susceptibility to poisons and further explain the instances of natural 
immunity to toxines. 
An example is given by Sachs,® who studied the reaction of guinea- 
pig blood against ‘‘arachnolysin,” a toxine found in spiders. In this 
case the complete immunit}^ of the red blood cells of the guinea pig 
against arachnol}^sin is accounted for by the entire absence of the 
proper receptors, while the susceptibility of the red blood cells of the 
rabbit to very small quantities of this poison 
is accounted for by the strong combining affin- 
ity which exists between these cells of the 
rabbit and the arachnolysin. 
In some cases the production of receptors 
ma}^ apparently be traced in the development 
of certain species. Cannus and Gley^ have 
followed the development (?) of the receptors 
in the red blood cells of the rabbit toward 
the hemolysin found in eel serum. Young- 
rabbits are much less susceptible to this poison 
than adult rabbits, which is accounted for by 
Ehrlich as being due to a gradual develop- 
ment of the receptors having proper combining affinities for the 
hemolysin fonnd in the eel serum. 
The union between the receptor of the cell and its poison is not 
always a direct one, as described above, but sometimes takes place 
Fig. Ig'.— The neutralization of 
a toxin by antitoxin; the free 
receptors in the blood have 
united with the io.x’m = anti- 
toxic immunity. 
« Sachs, Hans: Hofmeisters Beitr., bd. 2, h. 1-3. & Quoted by Ehrlich, loc. cit. 
