BY H. G. CHAPMAN. 55 



o 



simple mixture of these substances, that has to do with fixation 

 of complement. 



Moll,* Welsh and Chapman,! and Rodett have brought 

 forward much evidence to show that tlie precipitate or final 

 product of the interaction of antiserum and homologous protein 

 is mainly derived from the antiserum. Michaelis,§ in his recent 

 summary of precipitins, does not accept the general conclusion, 

 but grants that with the quantities employed by Welsh and 

 Chapman this conclusion holds. He writes "that these observers 

 have only had regard to mixtures of much precipitin and little 



precipitable substance and have rightly concluded that 



the precipitate consists wholly or almost wholly of the proteins 

 (Eiweisskorpfrn) of the precipitin serum." Now the quantities 

 of which Michaelis is writing show a much greater proportion of 

 homologous protein to antiserum than those employed by Muir 

 and Martin and other workers on deviation of complement. Dis- 

 regarding for the present purpose tlie source of the precipitate 

 under all circumstances, it can be accepted that the precipitate 

 which usually brings about deviation of complement is derived 

 mainly from the antiserum. It therefore follows that the amount 

 of complement deviated will be proportional to the amount of 

 antiserum used as antibody. It has been shown above that an 

 increase in the amount of antiserum leads to an increase in the 

 amount of precipitate, so that by increasing the amount of anti- 

 serum (antibody) deviation of complement may ha obtained with 

 smaller amounts of iiomologous protein. This factor has not yet 

 received attention in work upon deviation of complement. 



Remarks tivon the Practical A2jplicatio)is of the Precipitins. 



As pointed out in the introduction, the precipitin test was 

 applied early to tlie diagnosis of tlie source of blood-stains. 



* Quoted by Rodet, loc. cU. 



t Proc. Roy. Soc. London, B.lxxviii., p.310, 1906. 



X Comp. rend. Soc. Biol. Paris, p. 671, 1906. 



§ Oppenheimer, Handbuch der Biochemie, .Jena, 1909, Bd.ii., Hft. 1, S.565. 



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