402 THE CHEMICAL COMPOSITION OF THE BODY [CH. XXV. 



of egg, and others (pseudo-mucin and paramucin) are occasionally 

 found in dropsical effusions. 



Dr Pavy has shown that a small quantity of a similar carbohydrate 

 can be split off from various other proteids, which we have already 

 classified as simple proteids. 



3. NUCLEINS AND NuCLEO-PHOTEiDS. These are compounds of 

 proteid with a complex organic acid called nucleic acid, which con- 

 tains 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 characters 

 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 alkalis, 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 hsematogens (Bunge), of plant and animal cells. 



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

 is described in the next chapter. 



Nucleo-proteids may be prepared from cellular structures like 

 testis, thymus, kidney, etc., by two methods : 



1. Wooldridge's 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, 

 tissue fibrinogen. 



2. Sodium chloride method. The minced organ is ground up in 

 a mortar with solid sodium chloride ; the resulting viscous mass is 

 poured into excess of distilled water, and the nucleo-proteid rises in 

 strings to the top of the water. 



The solvent usually employed for a nucleo-proteid, whichever 

 method it is prepared by, is a 1 per cent, solution of sodium 

 carbonate. 



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

 characters are somewhat like those of mucin, but it differs chemically 

 in its high percentage of phosphorus. It is identical with the 

 chromatin of histologists (see p. 11). On decomposition, it yields an 

 organic acid called nucleic acid, together with a variable amount of 

 proteid. Nucleic acid on decomposition yields phosphoric acid and 

 various bases of the xanthine group. Some forms of nuclein, called 

 pseudo -nuclein, such as are obtained from casein and vitellin, differ 

 from the true nucleins in not yielding these xanthine compounds, or, 



