92 The Nature of Precipitin Reactions 



Eisenberg therefore concludes that precipitins contain two bodies, 



(a) which is labile and produces the visible reaction of precipitation, 



(b) which is stable and represents the haptophoric or combining group 

 of the precipitin, the part which possesses special affinity for the pre- 

 cipitable substance in the homologous serum. On theoretical grounds 

 Ehrlich (Croon. Lect., 1900) assumed the precipitins to possess such a 

 constitution, defining them as receptors of the second order (see p. 12), 

 and we find that Mtiller and Eisenberg reach the same conclusion in 

 consequence of their experiments. 



Eisenberg (p. 297) found inactivated antiserum to prevent pre- 

 cipitation by fresh antiserum both when it was added to precipitable 

 substance before, or when added simultaneously with, fresh antiserum. 

 In such a reaction there are three components, a. precipitable sub- 

 stances, b. heated antiserum, c. fresh antiserum. On adding a constant 

 amount of a mixture of a. and b. to a varying quantity of c., it will be 

 seen that the antagonism is overcome as the amount of c. added is 

 increased. Eisenberg notes that small amounts of b. are more anta- 

 gonistic than large amounts, which is not easy to understand, and 

 requires confirmation. He does not consider the antagonism due to the 

 action of b. on c., for the inactivated substance antagonizes best when 

 added to the precipitable substance before the active antiserum. In 

 other words, it does not antagonize as completely when added together 

 with fresh precipitin. From the fact that precipitation may be pre- 

 vented when b. and c. are added simultaneously, it seems clear that b. 

 has greater affinity for a. than has c. It is only when c. is in excess 

 that b. exerts a limited influence, this being due to the prepon- 

 derating amount of c. giving it a greater chance of being the first to 

 enter into combination with the precipitable substance. Where a 

 reaction is brought about by adding an excess of c., we have possibly to 

 deal with a " Massenwirkung " such as has been observed by Db'nitz, who 

 found that an excess of antitoxin apparently removed diphtheria toxin 

 which had already become anchored to body cells. 



Similar observations with regard to the bacterioprecipitins have 

 been made by Kraus and von Pirquet (5, vu. 1902, p. 68). They found 

 that the bacterioprecipitins for typhoid and cholera were inactivated by 

 heat (58 C.), and that such inactivated sera when added to fresh culture 

 filtrates prevented precipitation upon the addition of active bacterio- 

 precipitin. A fact which the authors state has been independently 

 observed by Pick. Inactivated precipitin was allowed to act for 10 hours 

 at 37 C. before adding fresh antiserum. They do not think that the 



