REP 



[ 383 



RET 



have red and cold blood, with true 

 lungs ; they are oviparous ; the 

 heart is trilocular, that is possesses 

 three cavities, namely, two auricles 

 and one ventricle. The brain of 

 reptiles is characterized by the 

 position of the thalami behind the 

 hemispheres ; neither is there any 

 arbor vitae in the cerebellum. Some 

 naturalists divide the class reptilia 

 into seven orders, namely, Chelonia, 

 Crocodilia, Lacertilia, Ophidia, 

 Dtnosauria, ~Enaliosauria, and J*te~ 

 rodactylia, the three last being ex- 

 tinct, and found fossil only. 



REPU'LSION. (repulsion. Fr.) That 

 property possessed by bodies which 

 causes their particles to recede from 

 one another, or to avoid coming in 

 contact. In air and in liquids, the 

 most perfect freedom of motion of 

 the parts among each other subsists, 

 and from this, and other considera- 

 tions, it has been concluded that 

 the several parts do not touch, but 

 are kept asunder at determinate 

 distances from each other, by the 

 constant action of the two forces of 

 attraction and repulsion, which are 

 supposed to balance and counteract 

 each other. 



RE'SIN. (resina, Lat. resine, Fr.) 

 Called also rosin. A yellowish- 

 white coloured substance, which 

 exudes from many trees, more 

 particularly the different species of 

 fir. It is somewhat transparent, 

 is hard and brittle, of a disagreeable 

 taste, and may be collected in con- 

 siderable quantities. Resin may 

 be distinguished from other sub- 

 stances by the following properties. 

 It is more or less concrete, and 

 possesses a certain degree of trans- 

 parency. Its taste is sometimes 

 hot and disagreeable, but not un- 

 frequently it is tasteless, or nearly 

 so. Colour generally between pale 

 yellow and brown. Specific gravity 

 from 1-0 to 1.3. It is electric and 

 a non-conductor of electricity. It 

 is insoluble in water, and by this 



may be distinguished, as well as 

 separated from gum. It is soluble 

 in alcohol, ether, and in the volatile 

 oils. There is scarcely a plant 

 which does not contain some kind 

 of resin. 



RESPIEA'TION. (respiratio,~La,i.} The 

 function of breathing; the act of 

 inhaling air into and exhaling it 

 from the lungs. Respiration con- 

 sists of two parts, inspiration, 

 which, in a healthy condition, 

 takes place about twenty-six times 

 in a minute, thirteen cubic inches 

 of air being the average quantity 

 taken in at each inspiration ; and 

 expiration, which alternates with 

 inspiration. It is by respiration 

 that the blood becomes freed of its 

 carbon and, at the same time, 

 obtains fresh supplies of oxygen. 



REST/PI^ATE. (resupinatus^ Lat.) In 

 botany, a term applied to leaves, 

 when the under surface is turned 

 upwards. 



RE'TE MUCO'SUM. (from rete, a net, 

 and mucosum, mucous, Lat.) A 



tissue lying immediately under the 

 epidermis, or scarfskin, and above 

 the eutis vera, or true skin. The 

 colour of negroes depends upon a 

 black pigment, situated in this 

 substance. 



RETEPO'EA.. The name given by 

 Lamarck to a genus of fossil corals. 



RE'TINA. (from rete, a net, Lat.) 

 The net-like expansion of the optic 

 nerve placed at the back of the 

 eye, and which has been called one 

 of the membranes of that organ. 

 Tli3 retina is an exceedingly thin 

 and delicate layer of nervous mat- 

 ter, supported by a fine membrane. 

 ]STo nerve but the optic nerve, and 

 no part of that nerve but the retina, 

 is capable of giving rise to the 

 sensation of light. 



RE'TINASPHALTTJM. A sub-species of 

 bitumen. An opaque, ochre-yellow, 

 and brittle substance found in 

 Bovey coal and fossil wood. Frac- 

 ture vitreous, and imperfectly con- 



