34 OSSEOUS TISSUE. 



to the true osseous tissue, is very inconsiderable in quantity, and 

 is, at all events, only mechanically mixed with it; it should 

 therefore, we think, be always merely compared with the quan- 

 tity contained in other bones, and not be included in the per- 

 centage representation of the chemical analysis as a constituent of 

 bone. The influence exerted by the fat of the true osseous tissue 

 on its physical properties has not as yet been accurately ascer- 

 tained. We have already spoken (in vol. i. p. 246) of the rules 

 which should be observed in the determination of the fats. 



In order to study the composition of the true osseous tissue 

 (and this has been the object of most of the analyses hitherto 

 made), the bones should in the first place be minutely pulverised, 

 carefully washed with water, and then deprived of their fat by the 

 action of ether ; for the analysis can yield no clear representation 

 of the composition of true bone until the fatty constituents, and 

 the substances soluble in water, and derived from the blood and 

 the bone-plasma, have been carefully removed. The presence of 

 these substances not only increases the difficulty of the technical 

 performance of the analysis, but the analysis itself naturally gives 

 only a very imperfect result in relation to the osseous tissue in 

 various physiological or pathological conditions. 



It was formerly customary to calculate the quantity of carbonate 

 of lime contained in bone by the quantity of lime in the fluid from 

 which the phosphate of lime had been precipitated (according to 

 Berzelius's method) by ammonia free from its carbonate ; but this 

 method has been shown by many analysts to be exceedingly 

 uncertain. The quantity of carbonic acid in the bones should 

 therefore always be determined by Fresenius's apparatus. It is 

 very useful to compare the quantity of carbonic acid contained in 

 the bones after they have been well washed and deprived of their 

 fat, with that present in the ash. We usually find rather more 

 carbonic acid in well-prepared ash than in fresh bone ; this excess, 

 which is slight in healthy bones, rises in some cases very con- 

 siderably in morbid bones. This is indeed the only method 

 which admits of our estimating how much lime is combined, not 

 with carbonic acid, but with organic matter. 



The method employed in preparing the bone-ash is not devoid 

 of importance ; for the determination of the earths, we must first 

 wash the pulverized bone and thoroughly remove the fat by ether, 

 and then after it is completely dried, submit it to the process 

 of combustion. Erdmann's muffle affords the most rapid and 

 complete means of incinerating bones ; burning them in a platinum 



