SUSCEPTIBILITY AND "IMMUNITY. 265 



ceptible to the toxic action of the other as if it did not possess this 

 immunity, i.e., the antitoxin of ricin does not destroy abrin, and 

 vice versa. As an 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 

 inflammakny 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 microorganism 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 inijcophylaxin 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* 



