ANALYSIS OF TISSUES. 



A. THE INORGANIC CONSTITUENTS. 



The analysis of the inorganic constituents in tissues can only be determined 

 after the organic matter has been removed by oxidation. The sulphur, 

 phosphorus, etc., which are present in organic combination, are oxidised to 

 sulphates, phosphates, etc., and are determined together with the sulphates and 

 phosphates which are present as such. The analyses of tissues which have been 

 performed have usually been effected after oxidation of the organic matter ; 

 consequently the data will include the amounts of these elements present in 

 organic combination. There is no satisfactory method of estimating these 

 elements in organic and inorganic combination separately, but comparative 

 data of very fair accuracy may be obtained by placing the tissue in alcohol 

 and boiling it for some hours on a water-bath to coagulate the proteins. The 

 alcohol is poured off and evaporated to dryness. The residue of protein and 

 also the alcoholic residue are extracted repeatedly with (i) ether, (2) water 

 or dilute acid (HNO 3 ) ; the aqueous extracts are combined and in these 

 extracts the elements are estimated as described under urine. The ex- 

 tracts may contain small quantities of organic matter, but these do not 

 seriously interfere. The ethereal extracts contain fats, lecithin, etc., in which 

 sulphur, nitrogen and phosphorus may be estimated (pp. 542, 555, 545). 



It is most usual to oxidise the organic matter by burning and to analyse 

 the ash which is so obtained. Special precautions have to be taken in pre- 

 paring the ash and the incineration is usually performed as follows : 



The material is dried in a platinum basin on a steam bath and weighed. 



The dry substance (about i gm.) is carefully heated with a small flame as 

 long as volatile and combustible substances are given off and the mass no 

 longer changes on further heating. The heating should not be above a dull- 

 red heat. The mass is allowed to cool and it is treated several times with 

 boiling water, each portion of water being poured off through a filter. The 

 aqueous solution is evaporated on a water-bath. The charred mass, together 

 with the filter paper, is dried and again heated in the basin to dull- redness. 

 The mass is boiled out with water, the aqueous solution added to the previous 

 one and evaporated. This process is again repeated and thus the soluble salts 

 are extracted. Heating at too high a temperature may result in a loss of 

 sodium and potassium chlorides. 



The extracted mass is heated to a higher temperature until all or nearly 

 all the organic matter has been oxidised. The residue is treated with boiling 

 water and the solution evaporated and combined with the previous ones. 

 The insoluble matter is dissolved in dilute hydrochloric acid. 



An aqueous and an acid extract are obtained. In these extracts the 

 elements are estimated according to the methods of inorganic chemistry, in 

 the same way as is described for the analysis of sodium, potassium, magnesium, 

 calcium, iron, phosphates, sulphates in urine (pp. 548, 546, 545, 542). 



The aqueous extract contains those salts which are soluble in water and 

 is generally alkaline owing to the presence of alkali carbonates and phos- 

 phates. 



Separate portions are tested and analysed for carbonic acid, sulphuric acid, 

 phosphoric acid, hydrochloric acid, sodium and potassium. Calcium sulphate 

 is occasionally found in the aqueous extract. The acid extract is tested and 

 analysed for calcium, magnesium, iron, phosphates, and sulphates. 



The most convenient method of analysing a tissue for the elementary and 

 inorganic constituents is to oxidise the material with sulphuric acid and nitric 

 acid and to analyse the solution as is described under urine. 



Sulphur cannot be estimated by this method, but the tissue is dis- 

 solved and partially oxidised by nitric acid, the final oxidation being effected 

 with copper nitrate in the same way as the analysis of total sulphur in urine. 



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