90 The Nature of Precipitin Reactions 



reaction. The tests conducted upon this precipitum will be considered 

 presently. 



Observation IV. A rabbit treated in the usual way with sheep- 

 serum, yielded an antiserum of which 25 c.c. took 4'5 c.c. of sheep-serum 

 to fully precipitate it. The washed precipitum weighed, when dry, "158 g. 



Observation V. Two rabbits were treated with horse-serum, receiving 

 6 and 5 injections each (55 and 45 c.c. total). Bled 3 days after last 

 injection. The mixed sera remained clear, and 40 c.c. thereof took about 

 5 c.c. of horse-serum to fully precipitate it. The washed precipitum 

 weighed when dry '366 g. 



Strube (12, vn. 1902) states that his results contradict those of 

 Biondi. Strube, like others, has found a quantitative relation to exist 

 between the interacting substances, for on adding 5 c.c. of a blood solu- 

 tion to different proportions of its homologous antiserum (1 : 10 to 

 1 : 5000) he obtained, as I have done, decreasing quantities of pre- 

 cipitum. In very dilute solutions, as Biondi is also stated to have 

 observed, large quantities of precipitum may apparently be formed, this 

 being attributed by Strube to the looser character of the precipitum 

 making it appear more than it actually represents. He also notes, that 

 by repeatedly adding an antiserum to blood dilution, and filtering each 

 time after precipitation takes place, fresh precipitations occur every 

 time antiserum is added, the amounts of antiserum of course being but 

 fractions of the total amount required to induce complete precipitation. 

 This also indicates very clearly that the reaction is quantitative and not 

 due to enzyme action. 



In activated A n tisera. 



Mtiller (18, II. 1902) found a lactoserum which had been inactivated 

 at 70 C. to have acquired the power of neutralizing precipitins, in the 

 sense that it prevented precipitation when active serum was added to 

 inactivated, the latter having been previously mixed with a given milk. 

 Lactoserum from which the precipitin had been removed by the addition 

 of casein is incapable of neutralizing active lactoserum. This indicates 

 that the neutralizing substances are not present in fresh lactoserum, 

 but that they are formed in consequence of heating. Inactivated normal 

 rabbit serum possesses no neutralizing power. The neutralizing sub- 

 stances are not affected by the presence of lime salts, and may be 



