ii 4 SCIENCE PROGRESS 



exact nature of these substances is still unknown, the general 

 view being that they represent merely additive compounds due 

 to the adsorbing power of the colloidal phosphatides. The 

 lecitho-proteins contained in the yolks of eggs have received 

 most attention. Hoppe-Seyler isolated from egg-yolk Vitcllin, 

 a protein showing a globulin nature, whilst R. H. A. Plimmer 

 has recently obtained another lecitho-protein from it, which in 

 distinction from vitellin is soluble in water. Jecorin, isolated 

 by Drechsel from liver, represents a compound of dextrose 

 with an unknown phosphatide, always containing sulphur. 

 The phosphatides of plants, which have been up till now con- 

 sidered as lecithins, contain in some cases as much as 16 per 

 cent, of a reducing sugar (galactose), as has recently been shown 

 by Winterstein. 



As a representative of the second class of phosphatides, the 

 di-amino-phosphatides, Sphingomyelin may be mentioned, which 

 was isolated by Thudichum from brain and which represents 

 the main phosphorised constituent of " Protagon." A similar 

 substance has recently been isolated by Bang and Forssmann 

 from the lipoids of red blood corpuscles, by Stern and Thierfelder 

 from egg-yolk, and by Erlandsen from heart muscle. 



2. The Cerebrosides are nitrogenous, but phosphorus free, 

 white crystalline substances which are nearly always found 

 together with the phosphatides. They are glucosides and furnish 

 on hydrolysis galactose together with fatty acids and bases. 

 The nature and constitution of the two latter cleavage products 

 have not yet been cleared up. Phrenosin, 1 and probably Kerasin, 

 are representative substances of this type, and they constitute 

 roughly 70 per cent, of the " Protagon " mixture. 



3. The most important member of the third group of 



Thudichum's classification is Cholesterin (cholesterol). It forms 



a constant and evidently essential constituent of protoplasm, 



and is found regularly in animal as well as in vegetable cells. 



In distinction from the phosphatides and cerebrosides it is 



easily obtained in a pure crystallised state. The identity of 



cholesterin from different organs and animals seems to be 



established. A substance has, however, been isolated, so far 



1 This name, introduced by Thudichum, is preferable to the better known term 

 M cerebrin," as the many different substances described by this name in the literature 

 are mixtures of partly hydrolysed cerebrosides (being prepared by boiling nervous 

 tissue with baryta). Gamgee's " pseudo-cerebrin " and Thierfelder's " cerebron " 

 are identical with phrenosin. 



