594 GLOSSARY. DUODENUM EXOGENOUS. 



the embryo has two cotyledons ; this division coincides with Ex- 

 ogenous Plants. 



DUODENUM. The part of the small intestine between the stomach and 

 jejunum. 



EFFERENT. 'See Afferent and Centrifugal. 



EMBRYO. The early stage of the young mammal in the womb ; the 

 same in the later stages is called foetus. 



ENCEPHALON. The parts of the nervous system contained within the 

 skull, composed principally of the cerebrum, the cerebellum, the 

 medulla oblongata, and the pons varolii. 



ENDOGENOUS. See Monocotyledonous. 



ENDOSMOSIS, EXOSMOSIS. When an organic membrane, or even a 

 porous mineral lamina, is placed between two fluids that differ in 

 density, the less dense fluid passes in large proportion to the side of 

 the membrane in contact with the denser fluid, while a less propor- 

 tion of the denser fluid passes in the opposite direction, till an equi- 

 librium of density is established. This is osmosis. Endosmosis is 

 the entrance into a vessel on this principle ; exosmosis the opposite. 



ENDOSPERM. See Albumen. 



ENERGY, CONSERVATION OF ENERGY. Whatever puts matter before 

 at rest into motion is an energy ; whatever accelerates the motion 

 of matter already in motion is an energy ; whatever stops or re- 

 tards the motion of matter in motion is an energy. There is 

 never any generation of energy out of nothing ; there is never any 

 loss of energy ; and this last proposition is what is signified when 

 the conservation of energy is spoken of. When two bodies of 

 equal magnitude and equal density are supposed to be moving 

 with equal velocity towards each other in free space in a straight 

 line, so that they must meet, their evident motion is extinguished, 

 and the united mass comes to repose. The amount of mechanical 

 motion which belonged respectively to each is resolved into heat 

 namely, the invisible movement of the particles of matter composing 

 each of the two masses, and the measure of heat produced, is in a 

 fixed ratio to the sum of the two velocities at the moment of collision. 



ENTOZOA. See Parasite. 



EPIGLOTTIS. A leaf-like cartilage which covers the orifice of the 

 larynx in deglutition. 



EPITHELIUM. A term originally applied to the cuticle or scarf-skin, 

 now employed to signify the thin outer covering of membranes in 

 general on their free surface. 



ETHYL, HYDRATE OF OXIDE OF. See Alcohol. 



EXCRETIONS. The excretions are those secreted matters which are 

 thrown off from the body as useless or hurtful, the only perfect 

 example of which, as a fluid, is the urine. 



EXOGENOUS. See Dicotyledonous. 



