64: PROXIMATE PRINCIPLES IN GENERAL. 



theirs. If we wish to ascertain, accordingly, the nature and proper- 

 ties of a saccharine solution, it will afford us but little satisfaction to 

 extract its ultimate chemical elements ; for its nature and properties 

 depend not so much on the presence in it of the ultimate elements, 

 oxygen, hydrogen, and carbon, as on the particular forms of com- 

 bination, viz., water and sugar, under which they are present. 



It is very essential, therefore, that in extracting the proximate 

 principles from the animal body, only such means should be adopted 

 as will isolate the substances already existing in the tissues and 

 fluids, without decomposing them, or altering their nature. A 

 neglect of this rule has been productive of much injury in the pur- 

 suit of organic chemistry ; for chemists, in subjecting the animal 

 tissues to the action of acids and alkalies, of prolonged boiling, or 

 of too intense heat, have often obtained, at the end of the analysis, 

 many substances which were erroneously described as proximate 

 principles, while they were only the remains of an altered and dis- 

 organized material. Thus, the fibrous tissues, if boiled steadily for 

 thirty -six hours, dissolve, for the most part, at the end of that time, 

 in the boiling water ; and on cooling the whole solution solidifies 

 into a homogeneous, jelly-like substance, which has received the 

 name of gelatine. But this gelatine does not really exist in the body 

 as a proximate principle, since the fibrous tissue which produces it 

 is not at first soluble, even in boiling water, and its ingredients 

 become altered and converted into a gelatinous matter only by pro- 

 longed ebullition. So, again, an animal substance containing ace- 

 tates or lactates of soda or lime will, upon incineration in the open 

 air, yield carbonates of the same bases, the organic acid having been 

 destroyed, and replaced by carbonic acid ; or sulphur and phospho- 

 rus, in the animal tissue, may be converted by the same means into 

 sulphuric and phosphoric acids, which, decomposing the alkaline 

 carbonates, become sulphates and phosphates. In either case, the 

 analysis of the tissues, so conducted, will be a deceptive one, and 

 useless for all anatomical and physiological purposes, because its 

 real ingredients have been decomposed, and replaced by others, in 

 the process of manipulation. 



It is in this way that different chemists, operating upon the same 

 animal solid or fluid, by following different plans of analysis, have 

 obtained different results ; enumerating as ingredients of the body 

 many artificially formed substances, which are not, in reality, 

 proximate principles, thereby introducing much confusion into 

 physiological, chemist^. 



