PRECIPITINS 185 



produce hut fcobl}' precipitating sera. Cantacuzene''" believes that 

 precipitins are formed chiefly in the lymphoid tissues and bone marrow, 

 and that the mononuclear macrophages are most active in their for- 

 mation." This view is supported by the observations of Hektoen,''^ 

 that anj'' agent that injures the bone marrow and lymphoid tissues 

 (e. (J., Roentgen rays), tends to interfere with antibody production. 



Apparently only proteins can pioduee precipitins; when split to 

 the peptone stage they lose this property, but the proteins of serum 

 resist tryptic digestion a long time before losing their precipitinogcnic 

 property,""* which is destroyed much more quickly by pepsin-HCl 

 mixtures. The precipitate itself is very resistant to disintegrative 

 agencies, including putrefaction (Friedbergor),^^ but is soluble in dilute 

 acids and alkalies. It has the power of binding complement (Gay)*'' 

 and if the complement causes solution of the precipitate, poisonous 

 substances are formed (Friedberger). Excess of antigen prevents the 

 formation of precipitate, or redissolves it, but excess of antiserum has 

 no effect. Since both reacting substances are colloids they follow the 

 laws governing other mutually precipitating colloids, and precipitation 

 occurs only when they are brought together in concentrations that lie 

 within definite zones of relative proportions. It is, of course, perfectly 

 possible to have a union of precipitin and antigen without any visible 

 ))recipitate occurring, since the product of the reaction is not neces- 

 saiily insoluble under all conditions; in this case the occurrence of a 

 reaction must be demonstrated by some other method, e. g., the com- 

 plement fixation reaction. At present it is not established that pre- 

 cipitins can be secured against lipoids or other non-protein substances. 

 Possibly precipitins can be produced for closely related substances with 

 molecules approximating in size the protein molecule, e. g., certain 

 substances present in supposedly protein-free filtrates of bacterial 

 cultures. As with the agglutinin reaction, electrolytes must be 

 present or precipitation will not occur. Neither the precipitin nor the 

 antigen seems to be altered appreciably by the reaction, since when 

 either is separated from the precipitate it retains its original properties. 



Since precipitation of colloids is accompanied by or dependent 

 upon an aggregation of their particles, the precipitin reaction is 

 closely related to the agglutination reaction. The amount of precip- 

 itation obtained is much modified b}^ the amount of inorganic salts 

 present, and, according to Friedemann,*^ there is a general resem- 



^5 Ann. Inst. Pasteur, 190S (22), 54. 



*^ Spleen tissue cultivated artificially in the presence of horse serum produces 

 specific precipitins for horse serum, and tissue from the spleen of a guinea pig 

 that has received injections of horse serum also develops precipitins for horse 

 serum when grown in cultures (Prvzgode, Wien. klin. Woch., 1914 (27), 201). 



^^ Jour. Infect. Dis., 1915 (17), 415; 1918 (22), 28. 



*^ Fleischmann, Zcit. klin. Med., 1906 (59), 515. 



" Cent. f. Bakt., 1907 (43), 490. 



50 See Univ. of Calif. Publ. Pathol., 1911 (2), 1. 



51 Arch. f. Hyg., 1906 (55), 361. 



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