288 LECTURES ON IMMUNITY 



One series of experiments was done with serum (A) 

 from horse blood and serum (B) from a calf which 

 had been treated with horse-serum several times. The 

 horse-serum was diluted with 50 times its volume of a 

 i per cent solution of sodium chloride. If to a certain 

 quantity, i c.c., of the calf-serum increasing quantities of 

 horse-serum (A) were added, at first no precipitate ap- 

 peared; then at higher concentrations of A the quantity 

 of precipitate increased nearly proportionally to the quan- 

 tity of A added until a maximum was reached. Thereafter 

 further additions of horse-serum caused the quantity of 

 precipitate to decrease until -at a certain limit the precipi- 

 tate again disappeared. This behaviour, which is very 

 common in reactions between sera and their precipitins, 

 is clearly apparent from the following figures. 1 In this 

 case the total volume (100 div.) of the capillary tube 

 was 0.04 c.c. The precipitate is therefore in the fol- 

 lowing table given in units of 0.0x304 c.c., corresponding 

 to one division. One c.c. of calf-serum is fixed as 100 

 units, corresponding to the fact deduced from the experi- 

 ments that it could yield in maximo 100 units of precipi- 

 tate, P\ and i c.c. of the diluted horse-serum is on 

 analogous grounds fixed as 300, so that i c.c. of A is 

 equivalent to 3 c.c. of B. This seems to indicate that 

 nearly the whole quantity of the albuminous substances 

 in A, but only a very small fraction of those in B, enter 

 into the precipitate. 



The maximum is reached at A = 100; that is, on the 

 addition of 0.333 c c - of horse-serum, the quantity equiva- 



1 Hamburger and Arrhenius: Proc. of the Meeting of the R. Ac. of 

 Sciences, in Amsterdam, May 26, 1906, p. 33. 



