465 



On Certain Phenomena of Inactivation and of Inhibition exhibited 



by Precipitin Antisera. 



By D. A. Welsh, M.A., B.Sc, M.D., Professor of Pathology, and H. G. Chapman, 

 M.D., B.S., Demonstrator of Physiology in the University of Sydney. 



(Communicated by Dr. C. J. Martin, F.R.S. Keceived April 30, — Read 



June 13, 1907.) 



(From the Physiological and Pathological Laboratories of the University of Sydney.) 



General Phenomena of Inactivation and of Inhibition exhibited by Heated 



Antisera* 



When a precipitin antiserum, prepared with blood serum or with egg white, 

 is heated to 75° C. for 10 or 30 minutes, it loses its power of yielding a 

 precipitate with the homologous protein (inactivation), and it acquires the 

 power, when added in sufficient proportion, of preventing the formation of the 

 precipitate that would otherwise appear when the homologous protein interacts 

 with unheated antiserum (inhibition). An identical heat exposure does not 

 produce the same degree of inhibitory power in different homologous antisera, 

 the inhibitory capacity being estimated by the amount of unheated antiserum 

 required to elicit a precipitate. 



In the majority of the antisera tested, inhibition was complete, that is, no 

 precipitation occurred, when (a) 0*1 c.c. heated antiserum, (b) 0*1 c.c. unheated 

 antiserum, and (c) 0*001 c.c. or 0*005 c.c. homologous protein were allowed 

 simultaneously to interact, or when (a) was mixed with either (b) or (c) for 

 24 hours before the other ingredient was added. Inhibition was always 

 complete when the amount of the heated antiserum was three times that of 

 the unheated antiserum, and always incomplete when these proportions were 



* Our conclusions are based on more than 1000 separate interactions, involving 

 20 different antisera, about 50 different combinations of heated and unheated antiser 

 having been tested. The antisera were prepared in the rabbit by intraperitoneal 

 injections of blood serum or of egg white. The general procedure was the same as that 

 indicated in a previous communication (' Eoy. Soc. Proc.,' B, vol. 78, p. 298, 1906), and 

 most of the interacting substances were employed in a fresh undried condition. To 

 obviate coagulation, the antisera were diluted with two or four volumes of water before 

 being heated, but this water is not included in the amounts of heated antiserum to which 

 reference is made in the text. Thus 0*1 c.c. heated antiserum indicates 0*1 c.c. antiserum 

 heated together with two or four volumes of water. We ascertained that the additional 

 water did not noticeably affect the interaction. 



