vin THE DENATURALISATION OF ALBUMLNS 343 



oxide Ag 9 0. This compound, which is soluble to the extent of 

 1 : 3000 parts of water, imparts to the latter an alkaline reaction, 

 owing to the formation of a hydrate which undergoes hydrolysis. 

 The author holds that the hydroxyl-ions, by uniting with potential 

 hydrogen-ions in the albumin-molecule, render the hydrogen-ions inert, 

 and thus prevent the coagulation by heat (see p. 318). Cohnheim 

 believes silver oxide to produce in the albumin-molecule a change 

 analogous to that induced by formaldehyde, i.e. the formation of 

 methylene compounds (see p. 250). 



Osmium Tetroxide. The author 1 discussed the oxidising action 

 of osmium tetroxide at the Anatomical Congress in Kiel in 1898, and 

 to this discussion Monckeberg and Bethe 2 refer in a paper, in which 

 they point out that osmium tetroxide is not able to form salts, and that 

 for this reason it does not cause coagulation, as do most other reagents. 

 They state, that by acting as an oxidiser, osmium tetroxide becomes 

 reduced to metallic osmium ; that white of egg treated with an equal 

 volume of 2 per cent Os0 4 remains fluid on being boiled, and that it 

 becomes unprecipitable by nitric acid, acetic acid, or alcohol, while it 

 is coagulated by a mixture of sublimate and nitric acid. Osmium 

 tetroxide, not being an electrolyte, has been used extensively by the 

 author for histological purposes, as it causes no structural change, 5 

 and even prevents sublimate from producing in the cytoplasm the 

 usual change brought about by electrolytes. The author's methods 

 have been adopted by Apathy and Bethe. 4 



Surface Action. Hermann 5 was the first to show that certain 

 albuminous substances, such as casein, nucleo-albumins, fibrinogen, the 

 paramyosinogens of different tissues, etc., are precipitated owing 

 to surface action, when burnt clay or animal charcoal is mixed with 

 their solutions. The same cause is at work, and therefore also leads 

 to precipitation, when milk is sucked through porcelain filters, for 

 Zahn, 6 and subsequently Lehmann, 7 have shown that the albumin 

 passes through the filter, while the casein becomes precipitated and is 

 held back by the filter. Picton and Linder 8 have found similarly 



1 Mann, Verhandl-. d. Anat. Gesellsch. Kiel, 1898, p. 39. 



2 A. Bethe and G. Monckeberg, Zeitschr.f. mikroskop. Anat. 54. 135 (1899). 



3 Mann, Zeitschr. f. wins. Mikr. 9. 481 (1894), and Physiological Histology, 1902, 

 pp. 69, 82, 102, 107, 128. 



4 A. Bethe and G. Mouckeberg, Zeitschr. f. mikroskop. Anat. 54. 135 (1899) ; A. 

 Bethe, Allgemeine Anat. u. Physiol. des Nervensy stems, Leipzig, 1903. 



5 L. Hermann, Pfiiigers Arch. f. d. ges. Physiol. 26. 442 (1881). 



6 F. W. Zahu, ibid. 2. 598 (1870). 



7 W. Hempel, J. Lehmaun's 'Milk Investigations/ ibid. 56. 558 (1894). 



8 H. Pictou and S. E. Linder, Journ. of the Cliem. Soc. 61. 148 (1892). 



