SUSCEPTIBILITY AND IMMUNITY. 265 
ceptible to the toxic action of the other as if it did not possess this 
immunity, 7.e., the antitoxin of ricin does not destroy abrin, and 
vice versa. Asan illustration of the fact, he states that in one ex- 
periment a rabbit was made immune for ricin to such an extent, that 
the introduction into its eye of this substance in powder produced no 
inflammatory reaction; but the subsequent introduction of a solution 
of abrin, of 1 to 10,000, caused a violent inflammation. 
Evidently these facts are of the same order as those relating to 
immunity from infectious diseases, and, taken in connection with the 
experimental data previously referred to, give strong support to the 
view that the morbid phenomena ‘in all diseases of this class are due 
to the specific toxic action of substances resembling the toxalbumins 
already discovered ; and that acquired immunity from any one of 
these diseases results from the formation of an antitoxin in the body 
of the immune animal. 
Hankin calls these substances produced in the bodies of immune 
animals ‘‘ defensive proteids,” and proposes to classify them as fol- 
lows: First, those occurring naturally in normal animals, which he 
calls sozins ; second, those occurring in animals that have acquired 
an artificial immunity—these he calls phylaxins. Each of these 
classes of defensive proteids is further subdivided into those which 
act upon the pathogenic microédrganism itself and those which act 
upon its toxic products. These subclasses are distinguished by the 
prefixes myco and toxo attached to the class name. 
In accordance with this classification a mycosozin is a defensive 
proteid, found in the body of a normal animal, which has the power 
of destroying bacteria. 
A toxosozin is a defensive proteid, found in the body of a normal 
animal, which has the power of destroying the toxic products of bac- 
terial growth. 
A mycophylaxin is a defensive proteid produced in the body of 
an animal which has an acquired immunity for a given infectious 
disease, which has the power of destroying the pathogenic bacteria 
to which the disease is due. 
A toxophylaxin is a defensive proteid produced in the body of 
an animal which has an acquired immunity for a given infectious 
disease, which has the power of destroying the toxic products of the 
pathogenic bacteria to which the disease is due. 
Buchner had previously proposed the name “alexins” for these 
defensive proteids. 
The importance of the experimental evidence above referred to in 
explaining the phenomena of natural and acquired immunity is ap- 
parent. The facts stated also suggest a rational explanation of re- 
