1906.] Main Source of " Precipitable " Substance, etc. 309 



In the first place equal volumes of various antisera prepared in the rabbit 

 and of the natural serum of several rabbits were dried to constant weight over 

 calcium chloride at 37° C. in vacuo, and weighed. In several instances the 

 mean of two concordant estimations was taken. The results are shown in 

 Table XI. 



The difference between the mean weight of antiserum and that of natural 

 serum becomes all the more striking when it is borne in mind that most of 

 the rabbits had lost weight during the process of immunisation, whereas the 

 control rabbits were all in good condition. 



We next examined by fractional heat coagulation two hen egg antisera 

 prepared in the rabbit, and compared them under the same conditions with 

 natural rabbit serum, with hen egg white, and with one of the above hen egg 

 antisera after interaction with hen egg white. In the last case 1"3 c.c. of 

 fluid hen egg antiserum reacted for 72 hours with 0'3 c.c. of 1-per-cent. hen 

 egg white in normal salt solution and yielded an abundant precipitate. The 

 clear superfluid was then removed, and treated in the same way as the other 

 substances investigated. 



The fluid antisera, sera, and egg white were diluted 20 times with normal 

 salt solution and acidified to an equal degree with acetic acid. Some 

 preliminary experiments were necessary to determine the most suitable 

 quantity of the latter. 



The results are given in the following table (XII), in which the lower 

 figure of each pair presents the temperature in degrees centigrade at which 

 opalescence was observed, the higher that at which flocculation and complete 

 precipitation occurred. Clear filtrates were obtained after each heating, and 

 from 30 to 40 minutes were allowed at each temperature to remove the 

 proteid. 



Table XII. 



Hen egg antiserum. 



Neutralised antiserum. 



Eabbit serum. 



Egg white. 



59—62 



53—60 



56—60 



59—62 







64—66 





68—70 



68—70 



69—70 



68—70 



71—72 









74—75 



73—74 



73—74 



72—74 



76—80 



76—80 



78—80 





84-86 



84—86 



82—84 





The figures indicate that in the antiserum there was present a body 

 coagulating at 72° C, and disappearing after inaction with egg white. The 

 precipitates that separated from the antiserum at this temperature and at 



