2B2 Professor Svante Arrhenius [June f>, 



X. — The Precipitins. 



Those organic substances which give a precipitate with some 

 albuminous substances are called precipitins, e.g. rennet, precipitating 

 casein from milk, is called a precipitin. But this name is often 

 i-eserved for such precipitating substances as are specific and have 

 been prepared by the injection of the albuminous substance in 

 question into the veins of an animal. Thus, for instance, the blood- 

 serum of animals injected with milk contains a precipitin against 

 milk, called lactoserum, which, like rennet, precipitates casein. It 

 has been studied carefully by Bordet and P. T. Miiller. 



Lactoserum is decomposed at about 70" C. As its compound 

 with casein is partially dissociated, heating to 70° C. for a certain 

 time decomposes the total quantity of the serum, so that the casein is 

 regenerated. The process as regards casein is wholly reversible. 

 Generally speaking, the processes investigated in immuno-chemistry 

 are reversible, but the treated substances are so easily altered, like 

 the lactoserum, that their composition is changed by secondary pro- 

 cesses, and it is therefore in most cases impossible to recover them 

 quantitatively. 



If we add casein in increasing quantities to a given quantity of 

 lactoserum, the precipitate increases to begin with, but is dissolved 

 again later on. The precipitate, which is obtained by adding in- 

 creasing quantities of egg-white to a given quantity of its precipitin, 

 according to Eisenberg behaves in the same manner. Evidently we ' 

 have to deal here with cases of chemical mass-action analogous to 

 those which we obtain when we add increasing quantities of an alkali 

 to different salts of certain metals, such as zinc, lead, aluminium, etc., 

 in which case we also at first obtain a precipitate, which later on 

 becomes dissolved. 



A special interest attaches to those precipitins which are obtained 

 through the injection of the blood-serum from one animal into the 

 veins of another. Their behaviour has been investigated quanti- 

 tatively by Hamburger in Groningen. As an instance, I give the fol- 

 lowing figures of Hamburger, regarding immune serum from a rabbit 

 injected with serum from a sheep. He mixed • 4 c.c. of the immune 

 serum with different quantities A (in c.c.) of sheep's serum (diluted 

 with 4'.) parts of 0"9 per cent. NaCl solution). After a while he de- 

 termined the quantity P of precipitate by centrifuging it down into 

 a narrow graduated tube. P is measured in units of 0*0004 c.c. 

 This quantity has been calculated by me according to the following 

 f oruuda : — 



'^OA-P . 120 - P _ 



This formula indicates that the precipitate is a compound of the 

 two sera. Every c.c. of the solution of sheep's serum is equivalent 



