74 ALAN ARTHUR BOYDEX. 



cipitins \vhen injected into animals. Bordet injected fowl blood 

 into rabbits and rabbit blood into fowls and obtained specific 

 antisera in either case. Tchistovitch injected eel serum and 

 horse serum into rabbits and obtained likewise antisera which 

 gave precipitins when mixed with the particular serum used for 

 injection. From these and many similar results obtained by 

 other workers it was learned that in general any foreign protein 

 was capable of stimulating precipitin formation when injected 

 into animals. 



Now such a specific reaction might be applied to the solution 

 of many biological and medical problems. It might be used to 

 identify unknown bacteria, to diagnose an obscure disease, to 

 detect the adulteration of meats, or to identify unknown blood 

 stains in medico-legal cases. Indeed, the precipitin reaction has 

 been used for all these purposes and for others as well. The 

 amount of work done in the solution of these problems is con- 

 siderable, and the literature dealing with them is extensive. 

 It is desired here, however, to mention only the more important 

 contributions to problems primarily zoological. 



To Uhlenhuth belongs the greater part of the credit for having 

 worked out a dependable method for the identification of un- 

 known blood stains in criminal cases. But in these early studies, 

 Uhlenhuth (1901) records results of importance to the zoologist. 

 It may be recalled that the precipitin reaction, as first known, 

 was entirely specific. Uhlenhuth noted, however, that the 

 reaction was not always strictly specific but that sometimes an 

 antiserum against one kind of protein would react not only with 

 this same protein (homologous reaction) but would also react, 

 though to a less degree, with other closely related proteins as well 

 (heterologous reaction). The precipitin reaction was thus proven 

 to be not strictly specific though in fact it remained quantitatively 

 so inasmuch as the homologous reaction was always stronger 

 than any heterologous reaction with the same antiserum. Uhlen- 

 huth then followed up this discovery with studies on the reactions 

 of various egg albumins and pointed out the value of studies of 

 this kind on related proteins. 



far the most important studies on related proteins have 

 XuUnll (1904). In his book "Blood Immunity 



