354 



PHYSIOLOGICAL CHEMISTRY 



(d) To about 5 c.c. of the solution in a test-tube add a few drops of dilute 

 hydrochloric acid and boil for a few moments. Now add a little barium chloride 

 to this solution. Is the precipitate any larger than that obtained in the preceding 

 experiment? Why? 



(e) To the remainder of the solution add a little dilute hydrochloric acid and 

 boil for a few moments. Cool the solution, neutralize with solid potassium 

 hydroxide, and try Fehling's test. Explain the result. 



IV. OSSEOUS TISSUE 



Of the solids of bone about equal parts are organic and inorganic 

 matter. The organic portion, called ossein, may be obtained by re- 

 moving the inorganic salts through the medium of dilute acid. Ossein 

 is practically the same body which is termed collagen in the other 

 connective tissues, and in common with collagen yields gelatin upon 

 being boiled with dilute mineral acid. 



In common with the other connective tissues bone contains a 

 mucoid and an albuminoid. Because of their origin these bodies are 

 called osseomucoid and osseoalbumoid. Osseomucoid, when boiled with 

 hydrochloric acid, yields sulphuric acid and a substance capable of 

 reducing Fehling's solution. The composition of osseomucoid is very 

 similar to that of tendomucoid and chondromucoid (see page 112). 



The inorganic basis of the dry, fat-free bone is a chemical substance, 

 not a mixture. This fact is indicated by the uniform composition of 

 the bones of fasting animals as well as by the definite relationship exist- 

 ing between the elements present. Bones of normal and fasting animals 

 of the same species present no profound differences in percentage com- 

 position. The percentage composition of the dry, fat-free femurs of two 

 dogs 1 after the animals had fasted for 104 and 14 days respectively was 

 as follows: 



The marked uniformity in composition notwithstanding the wide 

 variation in the fasting periods is significant. The tensile strength of 

 the femur of the dog has been found to be at least 25,000 pounds to the 

 square inch 1 whereas that of oak is 10,000 and that of cast iron 20,000 

 pounds to the square inch. 



1 Johnston and Hawk: Unpublished data. For data on a n 7-day fast by dog No. i, see 

 Howe, Mattill and Hawk: Jour. BioL Chem., n, 103, 1912. 



