1026 APPENDIX. 



they propose to designate as nuclo tides. When the phosphoric acid is split 

 off a compound of the carbohydrate and the nitrogenous base is left, and on 

 further hydrolysis the carbohydrate may be split off and various nitrogenous 

 substances be formed, such as purin bases or pyrimidin derivatives. These 

 final decomposition products are characteristic of the true nucleoproteins as 

 distinguished from the phosphorus-containing proteins, the nucleo-aibumins 

 or phosphoproteins, such as casein. The percentage of phosphorus in the 

 nucleoproteins varies, according to the complexity of the molecule, between 

 0.5 and 1.6 per cent. 



The ledthoproteins consist of compounds of the protein molecule with 

 lecithin (lecithans, phosphatids), while the phosphoproteins are compounds 

 of the protein molecule with some, as yet undefined, phosphorus-containing 

 substance other than a nucleic acid or lecithin. This group contains such 

 proteins as the vitellin of the yolk and casein of milk, which were formerly 

 designated as nucleo-aibumins. 



The Derived Proteins. — Under this designation are included products 

 derived from the simple proteins by hydrolysis. When the hydrolytic change 

 involves only a slight change in the protein molecule we have what are knowij 

 as primary derivatives, of which three groups are made: (1) Proteans, cer- 

 tain insoluble products which result from the incipient action of water, 

 enzymes, or very dilute acids. (2) Metaproteins, products which result from 

 the further action of acids or alkalies, by means of which the protein is con- 

 verted into a form soluble in weak acids or alkalies, but precipitated on neu- 

 tralization. This group includes what was formerly designated as acid or 

 alkali albumin. (3) Coagulated protein — insoluble products formed by 

 the action of heat, alcohol, etc. 



If the hydrolysis proceeds further, certain cleavage products result which 

 are simpler than these just named, but are more complex than the final 

 products of complete hydrolysis (amino-acids). These intermediate cleavage 

 products are grouped under the term secondary deri\'atives and include: 

 (1) Proteoses, products which are soluble in water, not coagulated by heat, 

 and are completely precipitated by saturation with ammonium sulphate or 

 zinc sulphate. (2) Peptones, products whicla are soluble in water, are not 

 coagulated by heat, and are not precipitated by saturation with ammonium 

 sulphate. (3) Peptids, products which consist of two or more amino-acids 

 in which the carboxyl group of one is united with the amino group of an- 

 other, with the elimination of a molecule of water. The peptones probably 

 are simply polypeptids or mixtures of polypeptids. 



DIFFUSION AND OSMOSIS. 



In recent years the physical conceptions of the nature of the processes 

 of diffusion and osmosis have changed considerably. As these newer concep- 

 tions have entered largely into current medical literature, it seems advis- 

 able to give a hriei description of them for the use of those students of phys- 

 iology who may be unacquainted with the modern nomenclature. The 

 very Hmited space that can be devoted to the subject forbids anything more 

 than a condensed elementary presentation. For fuller information refer- 

 ence must be made to special treatises.* 



Diffusion, Dialysis, and Osmosis. — When two gases are brought into 

 contact a homogeneous mixture of the two is soon obtained. This inter- 

 penetration of the gases is spoken of as diffusion, and it is due to tlie con- 

 tinual movements of the gaseous molecules to and fro within the limits of 

 the confining space. So also when two miscible liquids or solutions are 

 brought into contact a diffusion occurs for the same reason, the movements 

 of the molecules finally effecting a homogeneous mixture. If the two liquids 

 happen to be separated by a membrane diffusion will still occur, provided 

 the membrane is permeable to the liquid molecules, and in time the liquids 



* Consult Bayliss, "Principles of General Physiology," 1915; McClendon, 

 "Physical Chemistry of Vital Phenomena," 1917; Hober, " Physikalische 

 Chemie d. Zelle u. d. Gewebe." 



