108 A TEXTBOOK OF PHYSIOLOGY 



lished against various forms of poisons, vegetable or animal, bu1 in 

 particular against bacteria and the poisons they elaborate, which are 

 known as toxins. Two forms of immunity, then, may be acquired 

 one, which is the better understood, deals with the toxins, the second 

 deals with the bacteria themselves. In dealing with toxins the body 

 has the power to elaborate a group of substances which are known 

 as antitoxins. If at appropriate intervals and in appropriate doses an 

 animal's body be injected either (1) with one of the poisons or toxins, 

 produced in nutrient media by the growth of such bacteria as the bacilli 

 of diphtheria, tetanus (lockjaw), or (2) with vegetable proteins of a 

 poisonous nature, such as abrin (jequirity bean) and ricin (castor- 

 oil bean), or (3) with an animal poison, such as the venoms of 

 different forms of snakes, scorpions, bees, wasps, and spiders, a 

 specific antitoxin negativing the action of each of these poisons is 

 produced in the blood. 



It has been postulated that the living protoplasm consists of a central living nucleus 

 and numerous side chains, or receptors, which are attached to this. To each of these 

 one or other function is allotted above all, the absorption of nourishment. The side 

 chains, or receptors, form complexes of atoms in the molecules of the protoplasm 

 which, owing to their chemical structure, are able to combine or link up with other 

 substances for example, nutritive material, or toxirs. The receptors combine with 

 certain groups of atoms of these substances which, owing to their combining powers, 

 are termed haptophoric groups, or hlpiophors. The combination between these 

 haptophors of the nutritive material, or of the toxins with the receptors of the cells, 

 which have an affinity for them, is necessary before either the nutriment or the toxin 

 can have its effect on the cell. If when a toxin gams entrance within the organism 

 it finds no receptors of a structural substance to link with it, it can exert no poisonous 

 effect, and the organism is naturally immune to that toxin. Besides the haptophoric 

 group the toxin possesses a group which has the poisonous effect. This is the toxi- 

 phoric group, or toxophor. We may suppose that a nutritive group linking itself 

 to the central chemical nucleus of the cell helps to maintain the lability of the mole- 

 cular complex which manifests the phenomena of life, while a toxic group either 

 arrests the lability or shatters the molecular structure of this nucleus. 



The toxophor is harmless unless anchored on to the cell by the haptophor. 

 Just as a lock cannot be opened unless the person, the active agent, has the key. 

 Evidence has been obtained which makes it likely that these two groups do exist, 

 and that the toxin may lose its poisonous properties without losing its power of uniting 

 to the cells; thus, in the case of tetanus toxin it has bean shown that treatment with 

 carbon disulphide destroys the poisonous property of the toxin, but not its power 

 to evoke the production of antitoxin. The haptophoric group remain) linked with 

 the body tissue cells, and produce ; antitoxins by stimulating the production of re- 

 ceptors. Such a modified toxin is called a toxoid. Antitoxin s are cell -receptors 

 which combine with the haptophorous group of the toxin and render it harmless. 

 These cell-receptors are produced in great numbers, and set free in the blood by the 

 action of a toxoid, or by repeated small and non-lethal injections of a toxin. The 

 union of the haptophoric groups with the cell-receptors stimulates an increased pro- 

 duction of these cell-receptors which are secreted into the blood. Anti oxic sera arc 

 thus produced by the injection of toxoids or non-lethal doses of toxins. It is 

 suggested that the linkage of a chemical group with a particular side chain of a cell 

 evokes the production of other side chains of a similar configuration, and the production 

 of these may be stimulated to such an extent that they escape from the cell into the 

 blood and endow this with antitoxic power. The receptors (antitoxin) liberated 

 by any mammal immunized against a given toxin are apparently the same; thus, 

 the antidiphtheritic toxic serum of horse, sheep, or goat will, if injected, neutralize the 

 diphtheria toxin in another animal as, for example, the guinea-pig or man. But 

 each antitoxin is specific and will neutralize the toxin which produces it and no other ; 

 antidiphtheritic serum, for example, would be of no use if employed as the curative 

 agent for the toxin of tetanus. Every lock, so to speak, must have its own key, and if 

 the man has not the right key he cannot open the door. In this comparison the man 



