146 THE METHOD OF COMPLEMENT FIXATION. 



Ehrlich's idea of the biological structure of cells is that they consist 



Ehrlich's of two parts, a central functionating radicle ("Leistungskern") upon 

 Side Chain which depends the specialized activities of the cells, as for example, a 



Theory. glandular or nerve cell, and a multiplicity of side chains or receptors 

 (a term borrowed from the chemistry of the benzol group), by means 

 of which the cell enters into chemical relation with food and other substances brought 

 to it by the circulation. These receptors are exceedingly numerous, as the nutritive 

 substances upon which the cell depends for its maintenance are very varied. Besides 

 these general receptors the special cells also have different and special side chains; then, 

 too, there exist very great quantitative differences among the latter; and finally it must be 

 added that the selective activity of the cells depends upon the variability of these 

 receptors. 



When an infection occurs, pathological material is brought to the cell bodies instead 

 of physiological normal substances. Certain of these poisonous products find suitable 

 receptors in all of the cell groups, others fit only into distinct groups of cells, while a 

 third class are not taken up at all. This is strikingly in evidence, for the organism 

 which possesses no receptors for any of the pathological agents, cannot assimilate any 

 deleterious substances and is therefore immune. Lack of amboceptors is therefore a 

 natural form of immunity. The organism having only a special group of cells for the 

 reception of certain pathological matter, will make use of these cells for the binding and 

 assimilation of the toxic material. For example, the nerve cells alone have receptors 

 for tetanospasmin; no matter how or when the poison is introduced into the organism 

 the nerve cells will absorb it. As this toxin is poisonous for the central atom group 

 (Leistungskern) of the nerve cell, the latter is destroyed. The union between the nerve 

 cell receptors and the tetanospasmin toxin is only the preliminary act for the cell destruc- 

 tion; the actual death of the cell being caused by the action of the toxophore group of 

 the poison upon the functional radicle of the cell. If, however, such receptive side 

 chains are possessed not only by the brain but also by other cells, e.g., connective tissue 

 cells, the tetanospasmin will in part be bound by the latter. The toxophore group of 

 the toxin does not have any harmful effect upon the functional radicle of these cells, 

 and thus no toxic effects will be incurred by the union, and the nerve cells remain 

 unaffected. 



The number of receptors which cells possess for tetanospasmin, for example, are limited 

 and after their junction with the teanospasmin, are rendered useless and inactive. By 

 the normal reparative mechanism of the body, new receptors are generated. This 

 reparative process does not as a rule stop at a simple replacement of lost elements, but 

 according to the hypothesis of Weigert tends to overcompensation. The receptors 

 eliminated by toxin absorption are reproduced in an excess of the simple physiological 

 needs of the cell. Continuous and increasing dosage of the toxin soon leads 1o such 

 excessive production of receptors that the latter find no more room to be attached to the 

 cell, but are cast off and circulate free in the blood. They still, however, retain their 

 property of being able to combine with tetanospasmin. 



If such an organism is injected with tetanospasmin the latter toxin is bound by the 

 free receptors in the serum, and thus the respective "sessile" receptors attached to the 

 cells are precluded from coming in contact with the poison. Inasmuch as the free 

 receptors possess no functional radicle which can be injured, the toxin remains entirely 

 innocuous for the individual. Such protective bodies lend to the organism its attained 

 immunity and are known as antitoxins. Their function can be compared to lightning rods. 



v. Behring well expresses their action when he states that the same elements which 

 attached to the cells render the body susceptible to toxic substances, when circulating 

 freely in the blood serve to protect it. 



