INTRODUCTION 1 1 



ing the action of cholesterin. Saponin is a powerful 

 haemolytic agent. Its action is conditional upon the pres- 

 ence of cholesterin in the blood corpuscles. On the other 

 hand, cholesterin in the blood serum protects the blood 

 corpuscles from being attacked by saponin. Weigert 1 

 compared the cholesterin with a lightning conductor, which 

 has its proper place on the outside of the protected house. 

 From a chemical point of view we explain the observation 

 in the following manner. The membranes of the red 

 blood corpuscles are permeable to saponin, but not to cho- 

 lesterin or to the haemolytic compound of this substance 

 with saponin. Therefore the saponin is divided between 

 the blood corpuscles and the serum practically in propor- 

 tion to their content of cholesterin. If the content of 

 saponin-cholesterm in the blood corpuscles reaches a certain 

 amount, these are haemolysed, otherwise not. It is the 

 poison dissolved in the blood corpuscles that exerts an 

 action; the poison on their outside is without effect on 

 them. 



The first step in the development of sero-therapy into 

 an exact science consisted in devising methods for measur- 

 ing the quantities of the different substances employed. 

 In this regard Ehrlich enjoys great distinction in having 

 been the first who with sufficient exactitude measured the 

 strength of diphtheria-poison. To estimate justly the 

 great progress that was due to the introduction of measure- 

 ment methods by Ehrlich, it must be borne in mind that, at 

 the time that Ehrlich did his work, nearly all of the leading 

 men believed it impossible to measure toxins and anti- 



1 C. Weigert : " Einige neuere Arbeiten zur Theorie der Antitoxinimmuni- 

 tat," Wiesbaden, 1899. 



