6 00 HA CTER TO LOG Y. 



EHRLICH'S " SIDE-CHAIN " THEORY. The most re- 

 cent interpretation of the phenomenon of acquired im- 

 munity is that proposed by Ehrlich in 1897. ] It is 

 generally known as his " side chain " or " lateral bond " 

 (Seitenketten) theory of immunity. It is one of the most 

 attractive of all the hypotheses that have been advanced, 

 and is in many ways the most satisfactory. 



Its fundamental features comprise the acceptance of 

 Weigert' s doctrine concerning the mechanism of physio- 

 logical tissue-equilibrium and repair; and the assump- 

 tion of a specific combining relation, or affinity, between 

 toxic substances and the cells of particular tissues. 



At the meeting of German Naturalists and Physicians 

 held at Frankfort-on-the-Main, in 1896, Weigert 2 ad- 

 vanced an hypothesis the essential features of which 

 are that physiological structure and function depend 

 upon the equilibrium of the tissues maintained by virtue 

 of mutual restraint between its component cells ; that de- 

 struction of a single integer or group of integers of a tissue 

 or a cell removes a corresponding amount of restraint at 

 the point injured, and therefore destroys equilibrium and 

 permits of the abnormal exhibition of bioplastic ener- 

 gies on the part of the remaining uninjured components, 

 which activity may be viewed as a compensating hyper- 

 plasia ; that hyperplasia is not therefore the direct 

 result of external irritation, and cannot be, since the 

 action of the irritant is destructive and is confined to 

 the cells or integers of cells that it destroys, but occurs 

 rather indirectly as a function of the surrounding unin- 

 jured tissues that have been excited to bioplastic activity 



1 Ehrlich: Klinisches Jahrbuch, 1897, Bd. vi. Heft 2, S. 309. 



2 Weigert, Carl : " Neue Fragestellungen in der pathologischen Anat- 

 omic," Verhandlungen der Ges. deutscher Naturforscher und Aerzte, 

 1896, S, 121. 



