THE PROTEIDS 29 



^vhite of egg, and others called psetido-viucin and para-mucin are 

 sometimes found in the fluid of ovarian cysts, and dropsical 

 effusions. 



3. Nucleins and nucleo-proteids. — These are compounds of proteid 

 with a complex organic acid called nucleic acid, which contains 

 phosphorus. 



Nucleo-proteids. — Compounds of proteids with nuclein. They 

 are found in the nuclei and protoplasm of cells. Caseinogen of milk 

 and vitellin of egg-yolk are similar substances. In physical charac- 

 ters they often closely simulate mucin ; in fact, the substance called 

 mucin in the bile is in some animals a nucleo-proteid. They may be 

 distinguished from mucin by the fact that they yield on gastric 

 digestion not only peptone but also an insoluble residue of nuclein 

 which is soluble in alkahs, is precipitable by acetic acid from such a 

 solution, and contains a high percentage (10-11) of phosphorus. 



Some of the nucleo-proteids also contain iron, and it is probable 

 that the normal supply of iron to the body is contained in the nucleo- 

 proteids, or haematogens (Bunge), of plant and animal cells. 



The relationship of nucleo-proteids to the coagulation of the blood 

 is described under Blood. 



Nucleo-proteids may be prepared from cellular structures like 

 testis, thymus, kidney, &c., by two methods : — 



1. Wooldridges method. — The organ is minced and soaked in 

 water for twenty-four hours. Acetic acid added to the aqueous 

 extract precipitates the nucleo-proteid, 



or, as Wooldridge called it, tissiie fibri- ^ — — ~^ 



nog en. - .^*;^.i - 



2. Sodium chloride method. — The 

 minced organ is ground up in a mortar 

 with solid sodium chloride ; the result- 

 ing viscous mass is poured into excess 

 of distilled water, and the nucleo-proteid 

 rises in strings to the top of the water. 



ml. 1 I. n 1 J r ^"'- 9-— Diagram of a cell : u, proto- 



The solvent usually employed for a piasm composed of spon^opusm 

 nucleo-proteid, whichever method it is fntl^adi^^work o'^/'^hre'S^ 

 prepared by, is a 1-per-cent. solution of Suafer^f '^ ' """^ «', nncieoins. 

 sodium carbonate. 



Nuclein is the chief constituent of cell-nuclei. Its physical 

 characters are something like mucin, but it differs chemically in 

 containing a high percentage of phosphorus. Nuclein is identical 

 with the chromatin of histologists (see tig. 9). 



On decomposition nuclein yields a complex organic acid called 



