PRECIPITINS 155 



mentally produced. 1 Presumably the precipitin reaction is a 

 means of throwing such foreign proteids out of solution and 

 rendering them harmless. 



Precipitin appears in the blood generally about six days after 

 injection of the proteid, but disappears after injection of each 

 subsequent dose of proteid, to reappear again after a somewhat 

 shorter lapse of time. After injections are stopped, the precipi- 

 tin disappears rather rapidly, but never appears in the urine, 

 although it may enter the fetal blood from the blood of preg- 

 nant female animals. Leucocytosis, both local and general, 

 follows the serum injection, and it has been suggested that the 

 leucocytes are the source of the precipitin. The presence of 

 precipitins in the blood does not seem to prevent the excretion 

 of the foreign proteid in the urine, nor are the animals less 

 susceptible to the toxic action of the foreign proteid ; indeed, 

 the reaction is even stronger in the immunized animals, and 

 sometimes the ordinary dose becomes fatal, 2 as mentioned pre- 

 viously under " Toxicity of Serum." 



Chemical Properties. In its chemical nature precipitin re- 

 sembles the "antibodies" generally, being precipitated in the 

 euglobulin fraction of the serum, 3 and slowly destroyed by 

 trypsin, rapidly by pepsin. It cannot be separated from the 

 serum proteids. 



Specificity. As regards the specificity of precipitin reactions 

 certain points must be considered. Precipitin against human 

 albumin reacts with human globulin, but not with either horse 

 albumin or globulin. The groups that react, therefore, are 

 characteristic of the species, but common to different proteids 

 of the same species. This group does not occur in all proteids, 

 however, even in the same species, for precipitins against cow's 

 serum do not react with cow's milk. Bacterial precipitins 

 react frequently with members of an entire group. For ex- 

 ample, serum of animals immunized against B. typliosus may 

 produce precipitates in filtrates from cultures of numerous other 

 members of the colon-typhoid group, although quantitative 

 differences exist in favor of the form used in immunizing. 4 

 Likewise precipitins for the serum of one animal will produce 



1 Concerning the toxicity of egg-albumen, see Sollmann and Brown, Jour. 

 Exp. Med., 1902 (6), 207. 



2 See Rosenau and Anderson, U. S. Gov't. Dept. of Hygiene Bull., No. 29, 

 1906; Jour. Med. Research, 1906 (15), 179. 



3 Funck (Cent. f. Bakt. (ref.), 1905 (36), 744) states that if the precipitin 

 serum is very strong, part of the precipitin comes down in the pseudoglobulin. 



* For literature on Bacterial Precipitins see Norris, Jour, of Infectious Dis- 

 eases, 1904 (1), 463. 



