CARBOHYDRATES 25 



seems to be relatively inert chemically, and therefore is probably im- 

 portant only because of its effect on the physical properties of the 

 cells. By some it is considered to be a decomposition or cleavage 

 product of the proteins, which is in accordance witli its abundance 

 in masses of old necrotic tissue, e. <j., atheromatous masses, old in- 

 farcts, and old exudates. 



Protagon, which name probably covers a <;Toup of nitrogenous, 

 phosphorized bodies, (Gies),^- occurs in many or all cells, but espe- 

 cially in the nervous tissues. The properties of protagon are in gen- 

 eral similar to those of the other lipoids, but its exact composition is 

 too uncertain to permit of surmises as to its special purpose. 



Doubly Refractive Lipoids and Myelins.^' — In practically all nor- 

 mal tissues there are present droplets of lipoid nature which are 

 characterized b}^ showing prominent crosses when examined with 

 crossed Nicol prisms (anisotropic), the adrenal and corpus luteum 

 containing them most abundautl}^. Chemically they seem to be mix- 

 tures of various lipoids in inconstant proportions, but probably the 

 anisotropic character is most usually dependent upon the presence of 

 cholesterol esters. The term myelin was first applied by Virchow 

 to peculiar fatty substances found in various normal and pathological 

 tissues, because they showed physical characters similar to those of the 

 myelin substance of nerves, but as many of these substances are doubly 

 refractive, or can be easily made so, some authors use the term myelin 

 as if it were synonymous with doubly refractive lipoids. There are, 

 however, myelins which are not always doubly refractive, and also 

 double refractive lipoids which do not swell up in water to form 

 myelin figures, etc., as is characteristic of true myelins. Chemically, 

 however, the myelins and doubly refractive substances are probably 

 related, consisting of mixtures of cholesterol, cholesterol esters, lecithin 

 and perhaps soaps, in varjdng proportion. They will be considered 

 further in discussing Fatty ^Metamorphosis, Chap, xiv, 



CARBOHYDRATES 



The third great class of food-stuffs, the carbohydrates, is represented 

 in the cell by pentoses and Jiexoses combined with proteins and with 

 lipoids, and also by glycogen, which exists free. Glycogen is a rather 

 difficult substance to isolate in minute cpiantities and, therefore, al- 

 though it is not found in all cells by our present methods, yet it may 

 well be that it is a constant constituent of the protoplasm. There 

 is no evidence, however, that it is anything more than a source of 

 heat and energy to the cell. Its properties and occurrence will be 

 considered more fully in the discussion of glycogenic infiltration. 



12 Jour. Biol. Chem., 1905 (1), 50. 



13 See Adami, Jour. Amer. Med. Assoc, 1007 (48), 463: Karwicka. Ziepler's 

 Beitr., 1911 (50), 437; Schultze, Ergebnisse Pathol., 1909 (13, pt. 2), 253; Bang, 

 Ergebnisse Phvsiol., 1907 (6), 131; 1909 (8), 463. 



