THE PHENOMENON OF PRECIPITATION 267 



experienced workers, must be borne in mind and positive acceptance 

 of the colloidal explanations, however attractive, must be withheld 

 until much further investigation has been done. 



Another important and interesting phase of the study of precipi- 

 tins is that associated with the occasional presence in the same serum 

 of remnants of antigen and of precipitins which, though present 

 side by side, do not unite to form precipitates. This condition 

 is frequently seen in such sera as those produced by Fornet and 

 Miiller 49 for rapid precipitin production for forensic work, a 

 method in which the foreign serum is injected into rabbits in large 

 amounts (2 to 10 c. c.), on consecutive days, and the animals are 

 bled 6 to 8 days after the last injection. That such sera contain 

 both antigen and antibody is shown by the fact that, though clear 

 when taken, they will show precipitation not only when mixed with 

 dilutions of the antigen, but also when added to homologous precipi- 

 tating sera. 50 



This phenomenon has been noticed by Linossier and Lemoine, 51 

 Eisenberg, 52 Ascoli, 53 and others, and has been extensively studied 

 by von Dungern. 54 Gay and Rusk 55 have recently observed it in 

 connection with the rapid method of precipitin production of Fornet 

 and Miiller, and have noted that such sera, although containing both 

 antigen and precipitin, do not possess complement-fixing properties. 

 According to Uhlenhuth and Weidanz, 56 the antigen may persist in 

 the sera of protein-immunized animals, in demonstrable amounts, 

 as long as fifteen days after the last injection, and it is constantly 

 present during this period, but in progressively diminishing amounts. 



We are thus confronted by the apparently paradoxical phenom- 

 enon of the presence in these sera, side by side, of an antigen and its 

 homologous precipitin, incapable of reacting with each other, al- 

 though each of them readily reacts with precipitin or antigen, re- 

 spectively, when these are added from another source. 



Many attempts have been made to account for this. A number 

 of observers, notably Eisenberg, have concluded from extensive an- 



49 Fornet and Miiller. Zeitschr. f. biol. Technik u. Methodik, Vol. 1, 

 1908. 



so ;p or instance, a rabbit was injected on three consecutive days with 

 sheep serum. It was bled on the fifth day after the last injection. The 

 serum, was clear when taken, but a precipitate was formed when it was 

 added to sheep serum and also when it was added to serum from another 

 rabbit similarly treated and containing sheep serum precipitin. 



51 Linossier and Lemoine. C. E. de la Soc. de Biol., 54, 1902. 



52 Eisenberg. Centralbl f. Bakt., 34, 1903. 



53 Ascoli. Munch, med. Woch., Vol. 49, No. 34, 1902. 



54 Von Dungern. Centralbl f. Bakt., 34, 1903. 



55 Gay and Rusk. "Univ. of Cal. Public, in Pathology," Vol. 2, 1912. 



56 Uhlenhuth and Weidanz. "Praktische Anleitung zur Ausfiihrung, 

 tc.," Jena, 1909. 



