192 BACTERICIDAL OR ANTI-BACTERIAL IMMUNITY. 



to reinforce the present unsatisfactory methods of distinguishing between 

 human and other blood. For if one have a rabbit or other animal artifi- 

 cially adapted to human blood from which fresh serum can be secured 

 (even the dissolved dried serum will answer), he has only to dissolve in 

 a little salt solution a suspected blood clot, and, mixing the two, observe 

 the result. If under suitable conditions of dilution cloudiness develops 

 within a short time or if a precipitate be formed, it is claimed that the 

 suspected material could have been derived from no other animal than 

 man. Since, however, it has been found that the blood not only of 

 monkeys but of some other of the lower animals may give slight precipi- 

 tates under these conditions, and since other human fluids containing 

 albuminous substances, such as saliva, pus, inflammatory exudates, etc., 

 may also give precipitates, it is evident that the result of this test should 

 be interpreted with great caution. 1 



The white of a hen's egg injected into the peritoneum of rabbits after 

 a time gives rise to substances in the rabbits' serum which induces a pre- 

 cipitate in fresh solutions of hens' egg albumen. Xo precipitate is pro- 

 duced by this serum in albumen solutions from the blood of the mam- 

 malia, and only a slight precipitate is formed in the egg albumen of 

 related fowls, such as the duck, for example. 



It has been stated that by the adaptation of the living animal to ex- 

 tracts of muscle tissue from another species, precipitating substances 

 may be formed in the serum which are specific for the muscle used in the 

 injection. 



Milk of one animal thus introduced into the body of another gives 

 rise to a substance in the adapted animal which causes a precipitate in 

 the diluted milk used for injection, but not in the milk of another species, 

 save sometimes in slight degree in milk from closely allied animals. 



This reaction is also applicable to plant albumens. Thus, if an ani- 

 mal be adapted to a given species of bacteria, its blood-serum, on being 

 added to the clear filtrate of the pure culture, throws down a precipitate 

 which is in some instances light, in others voluminous. This reaction is 

 again specific, except within the group limits of related species. Thus, 

 as Morris has shown, 2 precipitating substances which are developed by 

 the adaptation of the rabbit to the typhoid bacillus induce a slight pre- 

 cipitate in the culture filtrate of the colon bacillus, but not in the filtrate 

 of B. prodigiosus, for example. 



Numerous experiments have shown that other vegetable albumens call 

 forth specific adaptive precipitius. 



This precipitation test is so delicate that it appears possible not only 

 to distinguish the albumens from different animal and vegetable species, 

 but to differentiate also some at least of the various albuminous sub- 

 stances in the individual. 



1 For a study of the precipitation test for blood, with bibliography, see Graham- 

 Smith, Jour, of Hygiene, vol. iii., pp. 258 and 354; also String and Straits*, Med. News, 

 November 7th and November 14th, 1903, bibl. ; also Robin, N. Y. Med. Jour, and 

 Pliila. Med. Jour., March 5th and 12th, 1904; also Nuttall's book, ref. above. 



2 florris, Jour, of Infect. Dis., 19l)4. 



