130 Immunity 



which it is anchored, are the chief cells by which it is absorbed. 

 In the alligator, however, other cells seem to fix the toxin before it 

 reaches or connects with those of the nervous system, so that the 

 alligator, though immune against the action of the toxin, is able to 

 make antitoxin as well as susceptible animals. 



Each introduction of appropriate antibody forming substance 

 is followed by an outpouring of the antibody far in extess of what 

 would neutralize it, so that after a systematic treatment has been 

 carried out for some time, the neutralizing value of the blood may be 

 a thousand times what would be necessary to neutralize the total 

 quantity of active substance introduced into the animal. 



Each antibody is specific in action, as must be evident from its 

 mode of formation. Should it be found, however, that several active 

 bodies possessed haptophores groups of identical structure, the anti- 

 body formed by any of them might be found to possess common 

 neutralizing powers for all. 



The animal whose blood contains antibodies enjoys immunity 

 from the active body by which they were formed only so long as 

 they are present. In some cases, however, animals that have 

 been long subjected to the immunization treatment, and whose blood 

 contains large quantities of free antitoxin, unexpectedly become 

 abnormally sensitive (hypersensitivity) to the toxin, and may die 

 after receiving a very small dose. This may be attributed to a 

 difference in the combining activity of the receptors attached to the 

 cells, and those separated and free in the serum. If the former 

 developed a greater affinity for the toxin than the latter, it would 

 unite with them by preference and intoxication ensue. If the treat- 

 ment by which the antitoxins are produced is interrupted, they im- 

 mediately begin to lessen in quantity, and eventually disappear. 

 Their occurrence in the blood determines that they should be found 

 in all the body juices, though in varying quantity. 



Their chemical composition, which experiment shows to be of 

 protein nature, determines that when practical use is to be made 

 . of them, they must not be administered by the stomach, as diges- 

 tion is usually followed by their destruction. In infants, the pro- 

 tein digestion being feeble, antitoxins pass from the mother's milk to 

 the blood of the sucking offspring without digestion, but the ad- 

 ministration of antitoxins by this method at later periods of life is 

 followed by effects too uncertain to be depended upon. For practi- 

 cal therapeutic purposes, therefore, the administration must always 

 be made hj^odermically or intravenously. 



Diphtheria Antitoxin.— This was first utilized for practical 

 therapeutic purposes by Behring.* As usually prepared by the 

 administration of the toxin, it is essentially an antitoxin and has 

 no destructive action upon the diphtheria bacilli. In therapeutics 



* "Deutsche med. Wochenschrift," 1890, Nos. 49 and 50; "Zeitschrift fur 

 Hygiene," etc., 1892, xii, p. i; "Die Blutserumtherapie," Berlin, 1902. 



