1 36 Immunity 



from its mode of formation. Should it be found, however, 

 that several active bodies possessed haptophore 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 anti-bodies 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 treatment by which the antitoxins are pro- 

 duced is interrupted, they immediately begin to lessen in 

 quantity, and eventually disappear. Their occurrence in 

 the blood determines that they shall be found in all the body 

 juices. 



Their chemical composition, which experiment shows to 

 be of proteid nature, determines that when practical use 

 is to be made of them, they must not be administered by 

 the stomach, as digestion is usually followed by their 

 destruction. In infants, the proteid digestion being feeble, 

 antitoxins pass from the mother's milk to the sucking off- 

 spring without digestion, but the administration of anti- 

 toxins by this method at later periods of life is followed 

 by effects too uncertain to be depended upon. For practical 

 therapeutic purposes, therefore, the administration must 

 always be made hypodermic ally or intravenously. 



i. Diphtheria Antitoxin. This was first utilized for prac- 

 tical therapeutic purposes by Behring.* As usually pre- 

 pared by the administration of the toxin, it is essentially 

 an antitoxin and has no destructive action upon the diph- 

 theria bacilli. In therapeutics it is employed to neutralize 

 or "fix" the toxin circulating in the blood, not to destroy 

 the bacilli, or to effect the regeneration of the tissues injuri- 

 ously acted upon by the toxin. Martin is of the opinion 



* "Deutsche med. Wochenschrift," 1890, Nos. 49 and 50; "Zeit- 

 schrift fur Hygiene," etc., xu, p. i, 1892; "Die Blutserumtherapie," 

 Berlin, 1902. 



