GLOSSARY Xlll 



munity due to vaccination, injection of toxin, etc., and is very variable 

 in duration. 



Precipitin. An antibody to a soluble form of proteid, having the power of 

 precipitating or coagulating that proteid by a process of clumping its 

 molecules. 



Precipitogen. The antigen to a given precipitin. Thus when a serum is 

 injected into an animal numberless substances are introduced, a certain 

 number of which only give rise to the formation of precipitin, and are 

 called precipitogens. Also called precipitable substance. 



Precipitogenoid. Heated precipitable substance, which has retained its 

 power of combining with precipitin, but no longer forms a precipitate 

 after doing so. 



Precipitoid. Precipitin which has lost its active or ergophore, but retained its 

 combining or haptophore, group ; the latter has also increased in 

 affinity for precipitable substance. The name is also applied to pre- 

 cipitogenoid. 



Predisposition. The opposite of immunity ; the state of an animal, in virtue 

 of which it is readily infected with a given agent. 



Preparator. Metchnikorf's term for immune body or amboceptor. 



Prophylaxis. Any process by which the vulnerability of an animal by an 

 infective agent or toxin is diminished or removed ; a process for the 

 induction of immunity, more especially in its practical application to the 

 prevention of disease. 



Prostatotoxin. A x cytolysin for the cells of the prostate. 



Pro-zone. In constructing a curve indicating the action of an antibody at 

 different dilutions, it sometimes happens that stronger solutions have 

 less effect than more dilute ones. The region of the curve in which this 

 inhibition of the action is brought about by an excess of the active sub- 

 stance is termed the pro-zone. It occurs with substances other than 

 antibodies. Also called zone of inhibition. 



Receptor. In Ehrlich's side-chain theory a part of a living molecule of pro- 

 toplasm which has the power of attracting and combining with a molecule 

 of food proteid (or of toxin, etc.) from the fluid with which it is bathed, 

 and of building it up into the whole molecule, and thus utilizing it as 

 nourishment, to aid which process it may also seize one or more 

 molecules of complement. When shed into the blood these receptors 

 constitute antibodies. 



1. Simple (e.g., those constituting antitoxin). In the antibodies formed 

 by this group we can only distinguish one group o'f atoms a haptophore 

 group having the power of combining with the specific antigen (e.g., 

 toxin), and preventing its subsequent union with a living cell, thus render- 

 ing it inert. 



2. Complex (e.g., agglutinin), in which we can recognize two separate 

 properties, presumably situate in different groups of atoms : (a) a hapto- 

 phore, combining group, as above ; and (b) an ergophore group, on 

 which the activity depends, and which may be destroyed whilst (a) 

 remains intact. 



3. Compound (e.g., amboceptor, on Ehrlich's theory). In them there 

 are t-uv or more haptophore groups, one of which combines with the 

 antigen, the others with one or more molecules of complement. 



Sensitization of bacteria, corpuscles, etc. The addition of immune body, so 

 that the objects are prepared or sensitized to the action of alexin. 



Side-chain theory. The theory (Ehrlich's) which accounts for the develop- 

 ment of antibodies by supposing that the receptors (q.v.) which combine 

 with the specific antigen may, under certain circumstances, be produced 

 in excess and cast off into the surrounding fluid ; these receptors, retain- 

 ing their power of combining with antigen, constitute the antibodies in 

 question. A brilliant conception, which has been the cause of enormous 

 advance in our knowledge of problems connected with immunity. 



