66 PHYSIOLOGICAL CHEMISTRY. 



When in a fluid state the fatty substances present themselves in the 

 form of drops or globules of various sizes, which may be recognized by 

 their optical properties. They are circular in shape, with a well- 

 defined outline. They often have a faint amber color, which is dis- 

 tinctly marked in the larger globules, less so in the smaller. As they 

 are more highly refractive than the watery fluids in which they are 

 immersed, they act as double convex lenses, and concentrate the light 

 transmitted through them at a point above the level of the liquid. 

 Consequently, they present the appearance of a bright centre sur- 

 rounded by a dark border. If the lens of the microscope be lifted 

 farther away, the centre of the globule becomes brighter and its bor- 

 ders darker. These characters will usually be sufficient to distinguish 

 them from other fluid globules of less refractive power. 



The oleaginous matters present a striking peculiarity in regard to 

 the form under which they occur in the living body, and by which they 

 are distinguished from the remainder of its ingredients. Instead of 

 combining with the other constituents of the animal solids and fluids, 

 in homogeneous union or solution, they are deposited, as a rule, in dis- 

 tinct masses or globules, suspended in the serous fluids, interposed 

 between the anatomical elements, included in the interior of cells, or 

 deposited in the substance of fibres or membranes. Even in the vege- 

 table tissues, they are always in the form of drops or granules. 



Owing to this fact the oils can usually be extracted by mechanical 

 means. The tissues are cut into small pieces and subjected to pres- 

 sure, by which the oil is forced out from the parts in which it was 

 entangled, and separated, without further manipulation, in a state of 

 comparative purity. A moderately elevated temperature facilitates the 

 operation by increasing the fluidity of the oleaginous matter ; but no 

 chemical agency is required for its separation. Under the microscope, 

 oil-drops an,d granules can be distinguished from the remaining parts by 

 their optical properties and by the action of ether, which dissolves them, 

 for the most part, without attacking other neighboring substances. 



In the adipose tissue the oils are contained in the interior of vesicles, 

 the cavities of which, in a state of health, they completely fill. The 

 adipose vesicle, which varies in diameter, in man, from 28 mmm. to 

 125 mmm., is composed of a thin membrane, forming a closed sac, in 

 which the oily matter is included. Sometimes, in cases of emaciation, 

 the oil partially disappears from the cavity of the vesicle, its place being 

 taken by a watery serum ; but the serous and oily fluids remain distinct 

 in the vesicular cavity. 



In the chyle, the oleaginous matter is in a state of emulsion, and its 

 subdivision is here more complete than anywhere else in the body. It 

 presents the appearance of a fine granular dust, known as the " molecu- 

 lar base of the chyle." A few of its granules measure 2.5 mmm. in 

 diameter ; but they are generally much less than this, and the greater 

 part are so small that they cannot be accurately measured. (Fig. 6.) 

 For the same reason they do not present the brilliant centre and dark 



