130 Immunity 



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 is immune against the action of the toxin, though 

 it is able to make antitoxin as well as susceptible animals. 



Each introduction of appropriate an ti- body forming sub- 

 stance is followed by an outpouring of the anti-body far in 

 excess of what would neutralize it, so that after a systematic 

 treatment has been carried out for some time, the neutral- 

 izing value of the blood may be a thousand times what would 

 be necessary to neutralize the total quantity of active sub- 

 stance introduced into the animal. 



Each anti-body is specific in action, as must be evident 

 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 they are produced 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 hypodermically or intravenously. 



