150 IMMUNITY. THEORIES OF IMMUNITY 



toxins and the production of antitoxins. It assumes that the side-arms 

 to a cell molecule are exceedingly numerous, not only because nutritive 

 substances are varied, but because special cells also possess different 

 and special side-chains, which anchor pathologic material. When 

 infection occurs, and in addition to toxins the physiologically normal 

 substances are brought to the cells, they likewise find suitable receptors 

 in practically all or certain cell groups, and become anchored, causing 

 more or less damage to the cells. 



Having combined with the side-arms or receptors of a cell, the toxin 

 may be sufficiently potent to kill the cell, and if a large number of cells are 

 so injured, symptoms of disease present themselves and death of the 

 infected host may follow. On the other hand, although the cell has lost 

 one or more of its side-arms, it may not be dead, and it proceeds at once 

 to repair the damage done. According to Weigert's "overproduction 

 theory/' nature is lavish in its processes of repair, and the cell not only 

 replaces the lost receptors, but produces them in numbers; the excess 

 receptors, having no space for attachment to the cell, are thrown off 

 into the blood-stream. Each of these cast-off receptors or haptines 

 possesses the same structure as the original receptor. These free re- 

 ceptors, then, are capable of combining chemically with their antigen, 

 neutralizing the antigen and rendering it innocuous. In diphtheria 

 and tetanus the antigen is largely the soluble toxin of the bacilli, and the 

 antitoxins are these cast-off receptors produced as a result of the stimu- 

 lating action of 'the toxins upon the cells. This excess of receptors is 

 made by repeatedly injecting a horse with increasing doses of diphtheria 

 toxin. By injecting this receptor-laden (antitoxin) serum into one 

 suffering from diphtheria, the receptors unite with free diphtheria toxin 

 and thus protect the body-cells. 



For the production of these receptors, or antibodies, as they are now 

 called, it is necessary, as previously stated, that the antigen enter into 

 chemical combination with the cell, so that the usual illustrations 

 showing the theoretic union of antigen and side-arm by physical contact 

 alone probably do not correctly portray what actually occurs. As 

 Adami points out, the antigen probably enters into intimate relation- 

 ship with the cell, and the continued stimulation of its presence is re- 

 sponsible for the production of an excess of receptors, in addition to 

 the overproductive tendencies of nature's repair. 



It is also necessary that the antigen possess sufficient toxic power at 

 least to stimulate the cell, for otherwise antibodies may not be produced. 

 Food material, for instance, being physiologic, is assimilated by the 



