34 PROXIMATE PRINCIPLES IN GENERAL. 



hepatic nerves. Lastly, two or more kinds of anatomical elements 

 interwoven with each other in a particular manner form a "tissue." 

 Adipose vesicles, with capillaries and nerve filaments, form adipose 

 tissue. White fibres, elastic fibres, and connective-tissue cells, with 

 capillary bloodvessels and nerve filaments, form connective tissue. Thus 

 the solid parts of the entire body are made up of anatomical elements, 

 tissues, organs, systems, and apparatuses. Every organized frame, and 

 even every apparatus, every organ, and every tissue, is made up of dif- 

 ferent parts, variously interwoven and connected with each other, and 

 it is this character which constitutes its organization. 



But beside the above solid forms, there are also certain fluids, which 

 are constantly present in various parts of the body, and which, from 

 their peculiar constitution, are termed " animal fluids." These fluids 

 are just as much an essential part of the body as the solids. The blood 

 and the lymph, for example, the pericardial and synovial fluids, the 

 saliva, which always exists more or less abundantly in the ducts of the 

 parotid gland, the bile in the biliary ducts and the gall-bladder : all 

 these go to make up the entire body, and are quite as necessary to its 

 physiological structure as the muscles or the nerves. Now, if these 

 fluids be examined, they are found to be made up of many different sub- 

 stances, which are mingled together in certain proportions ; these pro- 

 portions being constantly maintained at or about the same standard by 

 the natural processes of nutrition. Such a fluid is termed an organized 

 fluid. It is organized by virtue of the numerous ingredients which 

 enter into its composition, and the regular proportions in which these 

 ingredients are maintained. Thus in the plasma of the blood, we have 

 albumen, fibrine, water, chlorides, carbonates, and phosphates. In the 

 urine, we find water, urea, sodium urate, creatinine, coloring matter, and 

 salts. These substances, which are mingled together so as to make up, 

 in each instance, by their intimate union, a homogeneous liquid, are 

 called the PROXIMATE PRINCIPLES of the animal fluid. 



In the solids, furthermore, even in those parts which are apparently 

 homogeneous, there is a similar mixture of various ingredients. In the 

 hard' substance of bone, for example, there is, first water, which may be 

 expelled by evaporation ; second, lime phosphate and carbonate, which 

 may be extracted by the proper solvents ; third, a peculiar animal matter, 

 with which these calcareous salts are in union ; and fourth, various other 

 saline substances, in special proportions. The muscular tissue contains 

 water, sodium and potassium chlorides, lime phosphate, creatine, vari- 

 ous forms of albumen, and an animal matter termed myosine. The 

 difference in consistency between the solids and fluids does not, there- 

 fore, indicate any radical difference in their constitution. Both are 

 equally made up of proximate principles, mingled together in various 

 proportions. 



It is important to understand, however, exactly what are proximate 

 principles, and what are not such; for since these principles are ex- 

 tracted from the animal solids and fluids, and separated from each 



