88 PROXIMATE ANALYSIS OF 



one of innumerable varieties, all of which (within certain limits) 

 are equally likely to occur. It is by such a course alone that we 

 can hope to be able to deduce important and trustworthy con- 

 clusions regarding the state of the animal fluids in health, and 

 their various deviations from the normal standard, in diflerent 

 states of disease. 



A large number of perfectly distinct substances enter into the 

 composition of the blood and urine ; neither of these fluids can, 

 however, be regarded as true chemical combinations, but as 

 mixtures of many such combinations, which in their turn are 

 further subject to much variation. The study of these variations 

 in the blood and urine constitutes one of the most important 

 branches of animal chemistry ; but in consequence of the im- 

 mense labour attendant upon a complete analysis of these fluids, it 

 becomes expedient to confine our attention to their most impor- 

 tant constituents, in the same manner as the mineralogist seeks 

 only to determine the proportion of ore in a given quantity of a 

 mineral, or the vegetable analyst to ascertain the proportions of 

 sugar, gum, starch, and albumen, while he neglects the non-nu- 

 tritive substances, the fibre, acids, resins, colouring matters, &c. 



All compound animal substances that can fall within the 

 range of our investigation must be embraced in one of the fol 

 lowing classes, tlie solid, the fluid, or the gaseous. 



The animal fluids (to which we shall first devote our atten- 

 tion) diff'er extremely in their composition, but a general scheme 

 may be laid down for their investigation, if we previously know 

 that certain substances are not present, and therefore need not 

 be sought for. Thus, neither urea, uric acid, pepsin, nor bilin 

 will usually be sought for in the milk or in the brain, because 

 it is well known that their formation is limited to certain organs ; 

 neither will h^ematin, globulin, nor butyrin be looked for in the 

 bile, nor fibrin in the sweat or in the saliva, nor glutin nor 

 chondrin in any of the normal fluids. 



The principle upon which these investigations are conducted 

 is dependent on certain questions, which are to be answered by 

 the analysis. Thus in the analysis of the blood, the principal 

 component parts, the water, albumen, lipematin, globulin and 

 fibrin, are usually determined; but if it be requisite that the 

 analysis should be more fully carried out, we must separate the 

 haematin from the globulin, isolate the fats, extractive matters, 



