232 THE SOLIDS. 



4th. Being a bad conductor of caloric, it prevents the 

 too rapid dissipation of the heat generated in the system. 



5th. It is to be regarded as a reserve store of nourish- 

 ment set apart by the system during the period of its health 

 and strength, and designed to meet certain exigencies, when 

 the inherent powers of the constitution are called into re- 

 quisition, as in times of hunger and sickness. 



Distinctive Characters of Oil Globules. The contents 

 of fat vesicles are, as already stated, of an oleaginous 

 nature, which when they escape from the vesicles assume 

 the form of oil drops ; these are often met with in the 

 various fluids and solids of the system apart from the fat 

 vesicles, from which it is necessary that they should be 

 discriminated. There are several characters by which oil 

 globules may be distinguished from true fat vesicles ; thus 

 they are of a fluid nature, are usually perfectly spherical, 

 and on account of their fluidity, in place of being globular 

 are generally flat; they are seen sometimes to alter their 

 shape, as when they roll over on the surface of the object- 

 glass or come in contact with obstacles ; they reflect the light 

 less powerfully, and lastly, the slightest degree of pressure 

 causes them to coalesce. 



There is but little probability of confounding oil globules 

 with air bubbles ; these have a different colour, reflect the 

 light differently, and are perfectly globular. 



