viii HEAT-COAGULATION 321 



action. If large amounts of alcohol-salts be present, then an alcoholic 

 albumin solution will not coagulate. 1 



In practice one does not usually attempt to coagulate alkaline 

 solutions, as the calcium-albuminates are not quite insoluble, and as 

 the precipitation of alkali-albuminates requires a great deal of salt 

 and is even then not complete. The best plan to adopt is that 

 suggested by Cohnheim, 2 who adds to the albuminous solution to be 

 coagulated, firstly, sodium chloride or some other neutral salt, and 

 then an excess of acetic acid. If no salt is added, then the minutest 

 trace of acid in excess is sufficient to give rise to acid-albumin which, 

 remaining in solution, is converted into albumoses, if the boiling be 

 prolonged. If for any reason the addition of a neutral salt is contra- 

 indicated, then acetic acid should be employed, but only in minimal 

 quantities ; the reaction must be just perceptibly acid, so that the small 

 amounts of salt which are normally present may suffice for the pre- 

 cipitation. But even adopting all these precautions, one encounters 

 almost unsurpassable difficulties in coagulating muscle-albumins and 

 other organ-albumins. 3 



A neutral reaction of the fluid we wish to coagulate is only per- 

 missible if the albumin has been freed by prolonged dialysis as 

 thoroughly as possible from salts, acids, and bases (Cohnheim). 



Heat-coagulation is the only method we possess for separating an 

 albumin from its primary dissociation-products, and it is therefore 

 employed very frequently. For this very reason it is essential, if we 

 wish to precipitate the whole of the albumin, and if we do not wish to 

 form acid-albumins or alkali-albuminates, to keep the reaction of the 

 solution as feebly acid as possible, or to add a large amount of salt. 

 Disregard of these rules has led many observers, even up to quite 

 recent times, into making the most serious mistakes. 



9. Coagulation-Temperature 



If coagulation by heat is brought about in slightly acid solutions 

 or after the addition of sodium chloride and larger amounts of acetic 

 acid, it is found that each albumin has its specific coagulation-tempera- 

 ture. After many attempts had been made to define accurately the 

 coagulation-temperatures of egg-white and similar substances at the 

 beginning of last century, Kiihne 4 showed, in 1864, that two albumins 

 are present in muscle-plasma, one of which is coagulated at a much 



1 K. Spiro, Hofmeisters Beitrage, 4. 300 (1903). 



2 0. Cohnheim, Zeitschr.f. physiol. Chem. 33. 455 (1901). 

 :i W. His and W. Hagen, ibid. 3O. 350 (1900). 



4 W. Kiihne, Protoplasma und Kontraktilitat, Leipzig, 1864. 



