316 CHEMISTRY OF THE PROTEIDS CHAP. 



8. Coagulation by Means of Heat 



If watery solutions of albuminous substances are heated to a 

 certain temperature, the albumin becomes coagulated. Little as we 

 know as to the principles underlying this process, it is yet necessary 

 to discuss it in full, as we constantly have to practise it. 



Natural albumins are always changed chemically by heat action. 

 They become more basic, for distinctly acid solutions become less acid 

 and neutral solutions turn alkaline. On the other hand solutions of 

 muscle-proteids, which are essentially globulins, are rendered acid by 

 heat-coagulation, as was first shown for myosinogen and paramyo- 

 sinogen by Halliburton, and then fully confirmed by G. N. Stewart. 1 



The two main factors influencing heat coagulation are, firstly, the 

 reaction of the solution, and, secondly, the amount of salts present in 

 the solution. Apart from the older investigations of Lieberkiihn and 

 Heynsius 2 and others, the chief advance in more recent times has 

 been made by Fred^ricq, 3 Halliburton 4 and his pupil Hewlett, 5 

 Neumeister, 6 Brurmer, 7 and Starke. 8 They agree in emphasising that 

 complete precipitation and coagulation of albumin is only possible if 

 the reaction of the solution is slightly acid. Whenever the reaction is 

 too strongly acid or too strongly alkaline, then a greater or smaller 

 amount of albumin remains in solution and so escapes coagulation. 

 The other fact, first noticed by Aronstein, 9 and then confirmed by 

 Heynsius, 2 Harnack, 10 Billow, 11 Starke, 12 Pauli, 13 and Erb, 14 is shortly 

 this : If a solution of an albumin for example, egg-white has all 

 its inorganic salts removed by prolonged dialysis, then heat may 

 be applied without producing coagulation. But precipitation and 



1 G. N. Stewart, Journ. of Physiol. 24. 450 (1899). 



2 A. Heynsius, Pflugers Arch. f. d. ges. Physiol. 9. 514 (1874). 



3 L. Fredericq, a short summary is given in the Zentralbl. f. Physiol. 3. Nr. 23, p. 

 601 (1890). 



4 W. D. Halliburton, Journ. of Physiol. 5. 155 (1885). 



5 R. T. Hewlett, ibid. 13. 493 (1892). 



6 R. Neumeister, ' Introduction of Albumoses and Peptones into the Organisms, ' 

 Zeitschr.f. Biol. 24. 272 (1888). 



7 R. Brunner, Dissertation, Bern, 1894. 



8 J. Starke, ' Heat- Coagulation and Neutral Salts,' Sitzungsber. d. Gesellsch. f. 

 Morphol. und Physiol. in Miinchen, 1897, p. 1. 



9 B. Aronstein, Pfiuger's Arch.f. d. ges. Physiol. 8. 75 (1874). 



10 E. Harnack, Ber. d. deutsch. chem. Ges. 22. II. 3046 (1889) ; 23. II. 3745 

 (1890). 



11 K. Billow, Pfliiger's Arch.f. d. ges. Physiol. 58. 207 (1894). 



12 J. Starke, Sitzgsber. d. Ges. f. Morph. u. Physiol. in Miinchen, 1897, p. 1. 



13 W. Pauli, Pftiigers Arch.f. d. ges. Physiol. 78. 315 (1899). 



14 W. Erb, Zeitschr.f. Biol. 41. 309 (1901). 



