132 Seat of Origin of Precipitins 



I have made (p. 126) he found that a rabbit whose serum gave a dense 

 precipitum with a 1 : 500 dilution of egg-white before a fresh injection 

 of egg-white, only gave a faint clouding with a 1 : 200 dilution 24 hours 

 after another injection of egg-white. No deposit takes place in such 

 a serum when it is removed from the body. The solubility of a 

 precipitum in an excess of precipitable serum has been noted on 

 p. 89. 



The seat of origin of the precipitins is unknown. Michaelis and 

 Oppenheimer (1902, p. 356) followed up the clue which seemed to 

 be presented by the leucocytosis, (if one adopts the view of Metchni- 

 koff and his followers,) basing an analogy upon the origin they claim for 

 the cytolitic complements in the breaking up of leucocytes. Michaelis, 

 however, found precipitins circulating freely in the plasma, a fact which 

 does not lend support to the view that precipitins originate from 

 leucocytes. 



Biondi (1902, p. 15) sought to determine in which organs of 

 humanized rabbits the precipitins were formed. Having bled the animals 

 to death, he washed out the vessels with salt solution, cut up various 

 organs (liver, spleen, kidney, lung, brain, lymph glands, bone-marrow, 

 thyroid gland) and extracted these in saline. All the organ-extracts 

 contained precipitin, which he attributes to the possibility of blood 

 having been retained in the washed organs ; nevertheless the retroperi- 

 toneal lymph glands appeared to contain more precipitin than did the 

 other organs. 



Referring to the experiment in which Uhlenhuth succeeded in 

 obtaining precipitins for egg-white in the serum of a rabbit to which 

 egg-white had been administered per os, (an experiment which has 

 been confirmed for precipitins which act on blood, see p. 53,) Michaelis 

 (9, X. 1902, p. 734) notes that Uhlenhuth's antiserum only became rich 

 in precipitin after the rabbit had received many eggs. This points 

 to the probability of the precipitin being formed in consequence of the 

 excess of egg-white introduced, leading to quantities of it escaping 

 digestion. In other words, he thinks it is the non-assimilated egg-white 

 which stimulates the formation of precipitin. He pertinently adds 

 that if this were not the case, the serum of human beings, for instance, 

 those using milk as a part of their ordinary diet, would contain pre- 

 cipitins for milk, whereas as a matter of fact he has not found this 

 to be the case. 



I might add here that Hamburger (6, XI. 1902, p. 1190) observed 

 the rapid appearance of egg-white in the serum of a dog fed therewith, 



