274 CHEMISTRY OF THE PROTEIDS CHAP. 



may be mentioned, the coagulation of the caseinogen salts of calcium, 

 magnesium* barium, strontium, caffeine, and strychnine, which, accord- 

 ing to Osborne, 1 occurs between 35 and 45. 



2. Conglutination or Aggregation by Mechanical Means 



Berthold 2 observed in 1886 that 'mechanical coagula' may be 

 produced by shaking white of egg with distilled water, and that this 

 coagulum has the fibrillar appearance described by Flemming as 

 occurring normally in protoplasm. Ramsden 3 then found, quite 

 independently, that solid molecular aggregates of albumin may be 

 obtained by mere agitation of various albuminous solutions. 

 Filtered, clear solutions of white of egg, for example, on being shaken 

 in a test-tube soon form masses in the shape of long strands and 

 flocculi. The results of Ramsden have been criticised by Starke, 4 who 

 believes that these mechanical coagula are due to a drying of the 

 proteid solution whenever it comes into contact with air. To prove 

 his point he fills a bottle completely with proteid solution, drops in 

 pieces of glass rods, corks the bottle to exclude all air, and then shakes 

 vigorously for some weeks and obtains no coagula. Such an experi- 

 ment excludes, however, those very conditions as to surface tension 

 which are necessary for Ramsden's results (see below). 



The author 5 has explained the formation of mechanical aggregates 

 by assuming that the particles, which give rise to visible masses, adhere 

 to one another as would pieces of butter or any similar substance, on 

 being thrown together. The author introduced, for the purpose of 

 making a sharp distinction between chemical coagulation and the forma- 

 tion of mechanical aggregates for the latter, the term ' conglutination,' 

 and explained the formation of mechanical aggregates on shaking, for 

 example, a solution of egg-white in the following way : " The molecules 

 of white of egg in a dilute watery solution may be supposed to be evenly 

 distributed and spheroidal in shape. If in sufficient number to touch 

 one another, regular geometrical figures will result, as are seen, for 

 example, in foams, with this difference, that each space in the foam 

 must be imagined to be filled by one molecule of proteid. Such 

 solutions of 'proteid' appear clear, because all the molecules, being 

 symmetrically arranged, will form a homogeneous mass." 



"Where the solution is in contact with the air, as on its free 



1 W. H. Osborne, Journ. of Physiol. 27. 398(1901). 

 a Berthold, Studien iiber Protoplasmamechanik (1886). 

 :i Ramsden, Arch. f. (Anat. u.) Physiol. 1894, p. 517. 

 4 Starke, Zeit. /. Biol 40. 419 (1901). 

 3 Mann, Physiological Histology, 1902, p. 51. 



