THE PHENOMENON OF PRECIPITATION 263 



ever, because it has been impossible to isolate from organs their pe- 

 culiar, characteristic proteins, and immunization of animals with 

 organ extracts or solutions has necessarily implied the injection of 

 much blood protein and other albuminous material of a character 

 general to many organs of the animal, i. e., to the species. These 

 quantitatively overshadow the organ-specific substances which may be 

 present, and give rise, therefore, to a "species" precipitin. That 

 "organ specificity," however, is a fact has been shown by the experi- 

 ments of Uhlenhuth with the protein of the crystalline lens of the eye. 

 Immunization with this substance induces a precipitin which does 

 not react with the serum of the animal from which the lens was taken, 

 but does react, not only with the crystalline lens proteins of this spe- 

 cies of animal, but also with crystalline lens proteins in general, 

 though taken from another animal species. Analogous to this are the 

 experiments of von Dungern and others upon the protein derived 

 from the testicle. 



In both of these cases, as well as in other less sharply defined 

 examples, the specificity is attached, not to the species of animal, 

 but rather to the nature of the organ from which the particular 

 protein is derived. These facts first ascertained by means of the 

 precipitin reaction have been recently confirmed by means of the 

 reaction of anaphylaxis by Uhlenhuth and Haendel, and by Kraus, 

 Doerr, and Sohma. (See chapter on Anaphylaxis.) They have 

 been discussed, moreover, in connection with the problem of spe- 

 cificity in general. 



Biologically they probably signify that, although there are fun- 

 damental species differences between the general body proteins of 

 various animals, there are still, in certain highly specialized organs, 

 varieties of protein which, possibly because of functional exigencies, 

 have developed similar chemical characteristics. These have been 

 determinable by our present methods, however, only for organs like 

 the lens, the testicle, and the placenta from which the organ-specific 

 protein can be gotten in a relatively pure state. The pathological 

 importance of these phenomena lies in the fact that, although guinea 

 pig serum injected into a guinea pig will not give rise to antibodies, 

 lens protein apparently will do so an observation which opens the 

 possibility of autocytotoxins. The significance of this is indicated in 

 such investigations as those of Homer, 41 who, using the complement- 

 fixation technique to determine antibody, found that the serum of 

 adult human beings possessed antibodies for their own lens protein, 

 but that such antibodies were absent in the sera of children. 



The study of agglutination and that of precipitation reveal, 

 throughout, a close similarity between the two reactions, and indeed 

 in physical principles they are probably the same, although the one 



41 R6mer. Klin. Monatsbl. f. Augenheilkunde, Sept., 1906. Ref. from 

 "Weichhardt's Jahresber.," Vol. 2, 1906, p. 348. 



