458 VETEEINAEY HYGIENE 



which sets up the toxic action. The toxophore group may 

 be easily influenced whereby it loses its toxic properties, 

 and such a molecule is termed toxoid. 



In the same way the animal cell is considered to have, 



1. A stable central group. 



2. Unstable lateral groups. 



The stable toxin group or haptophore attaches itself to 

 the unstable lateral groups of the animal cell, while the 

 unstable, or toxophore group of the toxin in this way gains 

 access to the cell, which may mean its entire destruction. 



Thus the animal cell is likened to a side chain of atoms 

 in organic chemistry. These side, or lateral chains, also 

 called ' receptors ' (Pig. 187), under physiological conditions 

 are concerned with the assimilation of food, and are a 

 necessary condition for the nutrition of the cell. 



Under pathological conditions it is believed that the 

 haptophore group in the toxin is anchored or fixed to these 

 lateral chains, hence they are called receptors. The toxin 

 molecule being brought in contact with the cell, its toxo- 

 phoric group is now able to set up disturbances in the 

 protoplasm of the cell substance. 



By the union of the haptophore group of the toxin 

 molecule with the lateral chains of the cell, the side 

 chains only are destroyed, while the cell substance (the 

 central group), is unaffected and forms fresh lateral chains, 

 which accumulate in the general circulation. In fact an 

 excess of compensation occurs, which means an excess of 

 ' receptors,' which floating in the blood stream form the 

 antitoxin, and by laying hold of the toxin molecule, and 

 uniting with its haptophore group, prevents it from attack- 

 ing the cell substance. 



If a toxin and its antitoxin be injected into the blood at 

 the same time, the ' receptors ' pass into chemical combina- 

 tion with the haptophore group of the toxin molecule, and 

 a passive immunity is obtained which only lasts as long 

 as the side chains are present in the circulation. 



Natural immunity may be regarded as due to there being 

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