76 THE GENERAL CHARACTERS OF THE PROTEINS 



dilution contained in test-tubes of 53 x 7 mm., O'l c.c. of the pre- 

 cipitin containing serum, measured from a i c.c. pipette graduated in 



c.c., is added, the mixture is shaken and the series of test-tubes 



allowed to stand for one hour. The dilutions of the pure precipi- 

 tinogen and of the sample under investigation, which produce tur- 

 bidity within this time, are readily observed, and the quantity of 

 protein to be estimated can be readily calculated by the method 

 already described. The dilutions are arranged by Schulz according 

 to certain definite scales. The method has its limitations, for whereas 

 it can be successfully applied to the estimation of a given description 

 of muscular tissue in mixtures, even when the latter are not quite 

 fresh, it fails when applied to egg-proteins. 



The Complement Removing Action of Neisser and Sachs. The 

 following method was employed for distinguishing between human 

 blood and blood originating from other species. O'l c.c. of anti- 

 serum (i.e., serum of an animal immunised against human blood) 

 + 0*05 c.c. complement (fresh guinea-pig serum) + varying quan- 

 tities of normal sera of different origins, made up always to a volume 

 of I c.c. with physiological saline, were mixed and allowed to stand 

 for one hour at room temperature ; to each of the test mixtures was 

 added I c.c. of a 5 per cent, suspension of sheep's blood + 0*0015 

 c.c. of amboceptor-containing serum (serum of a rabbit immunised 

 against ox blood, such a serum acting haemolytically also towards 

 sheep's blood) ; the mixture was then allowed to stand at 37 C. 

 for two hours. Quantities of 'ooi c.c. of human serum caused total 

 inhibition of haemolysis ; in presence of similar quantities of serum 

 from monkeys a moderate amount of haemolysis took place ; whilst 

 much larger quantities (*oi c.c.) of sera from the rat, pig, goat, rabbit, 

 ox and horse were incapable of preventing complete haemolysis. 



A simplification of the above process is possible. Normal 

 rabbit's blood haemolyses sheep's blood, and this can be employed 

 instead of a prepared immune serum. It was found in Neisser and 

 Sachs* experiments that 0*25 c.c. of rabbit's serum could completely 

 haemolyse I c.c. of a 5 per cent, suspension of sheep's blood. 0*25 

 c.c. of this serum was, therefore, mixed with the liquid supposed to 

 contain human blood and the corresponding antiserum and allowed 

 to remain for one hour at 37. I c.c. of the 5 per cent, sheep's-blood 

 suspension was then added, and the mixture incubated again at 37 

 for two hours. The absence of haemolysis indicated the presence of 

 human serum. 



The principle of the method has been applied to the identification 

 of many proteins other than those contained in blood and serum. An 

 account of the researches with literature references is given in the 

 resumt of Blume. 



