576 CHEMISTRY OF THE PROTEIDS CHAP. 



there being formed albuminates, primary and secondary albumoses, and 

 peptones, and these, according to Tschermak, still give the two colour- 

 tests of amyloid, and in some instances even better than the original 

 mother substance. 



7. The Albumoids 



Under this name, which in reality is a but rarely used synonym 

 for albuminoid, Cohnheim has grouped a number of substances which 

 cannot be put into any of the other groups, and which possess a 

 number of properties in common. They form the membranse proprise 

 of many glands, the hyaline membranes, the sarcolemma, surrounding 

 muscle fibres, the firm constituents of the lens, of fish scales, etc. 

 Their number will no doubt be increased before long, and then . 

 further subdivision of this group may be made possible. The chemistr; 

 of these substances is practically unknown, because they can b 

 obtained only in very minute quantities. 



As regards solubility and digestibility they remind one of the 

 gelatine-yielding tissues, but they completely differ from them in not 

 yielding gelatine. In most respects they resemble coagulated albumin, 

 according to most authors. If albumin is coagulated and is then 

 exposed to dry heat of 115, it gradually becomes firmer, harder, and 

 less soluble, and finally nearly insoluble and indigestible, according to 

 Kuhne and Smith. 1 The albumoids about to be described resemble 

 such a coagulated albumin more or less, although, of course, this state- 

 ment does not in any way clear up the genetic relationship between 

 the albumoids and albumins. In other respects the albumoids differ 

 so much from one another as to necessitate their separate descriptions. 



Sarcolemma. Chittenden 2 has investigated its behaviour towards 

 digestive enzymes histologically, and has thereby shown that it differs 

 from the soluble muscle-albumins and from collagenous tissue. When 

 fresh it is readily digested by trypsin, but is rendered quite indigestible 

 by treatment with osmium tetroxide, while ordinary white fibrous 

 tissue remains soluble. The grey sheath of medullated nerves or the 

 sheath of Schwann ; the membrane propriae of the uriniferous tubules, 

 the gastric glands, and the pancreas ; the substance forming the lens- 

 capsule and Descemet's membrane in the cornea all behave similarly to 

 the sarcolemma. v. Holmgren 3 has found that after the removal of 

 the soluble constituents of muscle, there remains a fraction which is 



1 H. Smith, Zeitschr.f. Biol. 19. 469 (1893). 



2 E. H. Chittenden, Untersuch. a. d. Heidelberger physiol. Institut, 3. 171 (1879) ; 

 also H. F. A. Sasse, ibid. 2. 433 (1877). 



3 J. F. v. Holmgren, Malys Jahresber. f. Tierchem. 23. 360 (1893). 



