BODY TISSUES AND FLUIDS 467 



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Chondrosin has a very strong reducing action, which is due to a hexosa- 

 mine, named by Levene and La Forge chondrosamine, since it is isomeric 

 but not identical with glucosamine. Levene (c) has recently shown that it 

 is a derivative of galactose. Glucuronic acid is also present in the molecule 

 of chondroitln-sulphuric acid. 



The organic intracellular substance of bone is very similar to cartilage. 

 It differs in its very large deposit of inorganic salts, which normally con- 

 stitute about 40 per cent of the dry weight of the tissue. The ossein of 

 bone differs in no essential from the collagen of the other tissues men- 

 tioned. Likewise the osseomucoid and osseo-albuminoid are similar to 

 those found in tendon and cartilage. The inorganic material of bone is 

 chiefly calcium phosphate and carbonate, but magnesium is present and 

 also traces of fluorid and chlorid. McCmdden has given the following 

 figures for the important inorganic constituents of normal human bone 

 and bone from a case of osteomalacia : 



Brain 



The adult human brain weighs about 1200 to 2000 grams, of which 

 approximately 19 per cent is water. It contains from 100 to 120 grams 

 of protein after the extraction of the various lipoids. The brain as a 

 tissue is characterized by its very high content of lipoids, i.e., alcohol and 

 ether soluble material. The first worker to make real progress in the 

 chemistry of the brain was Thudichum, who published a most important 

 monograph on the subject in 1884. Of more recent work the studies of 

 Waldemar Koch (a) deserve special mention, while very important con- 

 tributions regarding the constitution of many of the lipoid compounds 

 of brain tissue have recently been made by Levene and his coworkers. 



Among the solid constituents of brain tissue are proteins, phosphatids 

 (lecithin, cephalin, etc.), cerebrosids or galactosids (phrenosin and cera- 

 sin), cholesterol, collagen, extractives and inorganic salts. Three dis- 

 tinct proteins, two globulins and a nucleoprotein, have been isolated from 

 the brain. The globulins coagulate at 47 C. and at 70-75 C., while 

 the nucleoprotein coagulates at 56-60 C. The lipoids are of particular 

 interest and will be specially considered. These bodies, as their name 

 would imply, resemble fats in some of their physical properties and 



