CHEMICAL INGREDIENTS OF THE BODY. 31 



the abnormal products of their change or decomposition. The substances 

 in question must be extracted from the tissues and fluids of the body 

 by the aid of physical and chemical manipulations, such as evaporation, 

 solution, precipitation, and crystallization. Many of them are of a nature 

 to be altered or decomposed by the treatment to which they are subjected, 

 or even by the unnatural conditions resulting from the cessation of life. 

 The coagulable substances of the blood and of the muscular tissue, which 

 are fluid during life, soon after death pass into the solidified condition, 

 and thus no longer present their original characters. The red coloring 

 matter of the blood requires to be extracted at a temperature nearly as 

 low as the freezing point of water, otherwise it loses its natural com- 

 position and becomes changed into other substances. The normal 

 coloring matter of the retina is bleached by the action of daylight, 

 and so disappears altogether unless special precautions be used for its 

 protection. This sensibility of the organic ingredients, making them 

 liable to be affected by unnatural conditions, is the reason why many 

 of them have long remained unknown or misunderstood ; and it also 

 accounts in great measure for the,changing nomenclature of physiological 

 chemistry. By improved methods of extraction, an organic ingredient 

 is often obtained in a new form, which more fully represents its normal 

 character ; and it therefore receives a different name, to distinguish it 

 from the former substance. Thus, the coloring matter of the red blood- 

 globules, formerly known as "hematine," was obtained from the blood 

 in an insoluble condition by the use of heat and acids. Subsequently, 

 when extracted by the simpler action of water and alcohol, at low 

 temperatures, retaining its natural color, solubility, and spectroscopic 

 character, it was named " heinoglobine," and was recognized as the 

 real constituent of the red globules. 



The physiological ingredients, therefore, of the animal frame are 

 substances which exist in its solids or fluids under their own form, and 

 are obtained by means which do not change them into other matters 

 or decompose them into their chemical elements. Lime phosphate, 

 for instance, is an immediate constituent of the bony tissue, but phos- 

 phoric acid is not so, for it is not present under its own form, but is 

 obtained only by breaking up its combination with the calcareous mat- 

 ter; while phosphorus is a product of still further decomposition of the 

 phosphoric acid. An animal substance containing the alkaline acetates 

 or lactates, if treated by incimeration in the air, would yield as a residue 

 the carbonates of the same bases, the original organic acids having been 

 destroyed and replaced by carbonic acid. As a rule, accordingly, in the 

 examination of animal tissues, the simplest forms of chemical manipu- 

 lation are most successful. The substance or fluid is first subjected to 

 evaporation, in order to extract and estimate its water. The evap- 

 oration is conducted at a heat not above 100 C, or the boiling point 

 of water, since a higher temperature would often be injurious to the 

 organic ingredients. From the dried residue sodium chloride, alkaline 

 sulphates, carbonates, and phosphates are extracted with water. Coloring 



