REST-HARROW. 



RHAMNACE.E. 



86 



With regard to the quantity of oxygen consumed during respiration 

 it was at one time supposed to be exactly equal to the quantity fount 

 in the carbonic acid expired. This however is not the case, for accu 

 rate experiments show that, after all allowance made for oxygen present 

 in the tissues, there is constantly a small quantity more taken into the 

 lungs than is thrown out. The destination of this oxygen is undoubt 

 edly to be found in the carbonic acid gas thrown out from the lungs 

 in the formation of the substances found in the bile and urine, anc 

 in the formation of phosphoric and sulphuric acids. The quantity 01 

 oxygen consumed is nevertheless measured by the carbonic acid thrown 

 off from the lungs, so that, where there is an increase of excretion ol 

 carbonic acid, there is an increase of absorption of oxygen. It is an 

 interesting fact that small animals consume a relatively much greater 

 proportion of oxygen gas than larger ones. It is also a fact of prac- 

 tical importance, that the quantity of carbonic acid gas exhaled is not 

 increased by increasing the quantity of oxygen in the atmosphere. 

 As a proof of the necessity of the changes involved in the absorption 

 of oxygen gas, it has been found that the eggs of birds, and undoubt- 

 edly this applies to the eggs of all animals, absorb oxygen and give 

 out carbonic acid. The following table gives the result of some 

 experiments of Valenciennes on this subject : 



The nitrogen of the atmosphere appears to act as a diluent, and to 

 temper the activity of the oxygen gas. Although when animals are 

 placed in atmospheres of pure oxygen, or hydrogen, a certain quantity 

 of nitrogen is thrown out from their lungs, it still requires proof 

 that this has been taken up from the atmosphere. It is not im- 

 probable that a certain quantity of nitrogen may be thrown off 

 by the decomposition of the nitrogenous tissues in the blood or 

 excretions. 



With regard to the watery vapour which passes off from the lungs, 

 it may be stated as a general rule that it is sufficient to saturate the 

 expired air. IU absolute amount is therefore influenced by the fol- 

 lowing circumstances : 1, By the volume of air expired ; 2, by the 

 quantity of watery vapour contained in the air previous to its inspi- 

 ration ; 3, by the temperature of the expired air ; 4, by the length of 

 time which each volume of inspired air is allowed to remain in the 

 loaf. 



We have thus considered the principal physical and chemical pheno- 

 mena presented during the respiration of animals. It should however 

 be recollected that these phenomena are dependent for their existence 

 on the influence of the nervous system. All the respiratory move- 

 ments effected by the muscular tissues, as far as they are independent 

 of the consciousness of the individual, are under the absolute govern- 

 ance of that part of the brain which is called the medulla oblongata. 

 It is this portion of the nervous system which acts as the centre of all 

 the impressions which convey the necessity of breathing, and which 

 initiates all the motions which result in respiratory action. [NERVOUS 

 SYSTEM; BBAIX] 



(Kirk es and I'aget, Handbook of Phytiology ; Lehmann, Phyiio- 

 loyical Chemistry, translated for the Cavendish Society by Dr. Day 

 Valentin, Text-Book of Phytiology, translated by Dr. Brinton.) 



REST-HARROW. [O.voxis.] 



RESTIA'CE^E, Cordleaft, a natural order of Plants, principally 

 inhabiting the southern hemisphere, and nearly related to Cyperace(e. 

 They abound at the Cape of Good Hope and in Australia, where they 

 form a hard wiry rush-like herbage. They have not been found in 

 America. They have in general a scaly creeping rhizoma, or root- 

 stock ; simple stems clothed with the sheaths of abortive leaves ; and 

 glumaceous flowers with a tolerably regular structure. The floral 

 envelopes generally consist of 4 or 6 glumes in two rows. The 

 stamens are 2 or 3 ; the ovary for the most part 2-3-celled, with a 

 single ovule in each celt The fruit is either a nut or a 3-celled seed- 

 vessel ; the seeds are pendulous, and the embryo is a small lenticular 

 body lying within albumen at the end of the seed most remote from 

 the hilum. In almost all cases the sexes are separate. The hard 

 texture of some species renders them suited for thatch for houses, 

 but they are of no other use. There are 23 genera and 171 species of 

 this natural order. 



RFTE'PORA. [POLYZOA.] 



RETI'FERA, a family of Mollutca. 



RETINA. [EYE.] 



RETINALITE, a Mineral, having a resinous appearance, found with 

 and allied to Serpentine. It is found at Oranville in Upper Canada 

 (Dana.) 



RETINASPHALTUM. [RETINITK.] 



e 2 1 



Ecslia tetraphyllui. [RESTIACK*.] 



1, the male : a, the stamens and abortive ovary ; fc, the same inclosed within 

 the floral envelopes. 



2, the female . c, the flower ; d, the ovary with abortive stamens ; <, a sec. 

 tion of the ripe seed, showing the embryo. 



RETINITE, a Mineral Reain. It occurs in roundish masses. Its 

 colour is light yellowish brown, green, or red ; lustre earthy or 

 slightly resinous in the fracture. It is sub-transparent to opaque. 

 Often flexible and elastic when first dug up, but loses these qualities 

 on exposure. Its hardness is 1-2-5, and its specific gravity 1-135. It 

 takes fire, and bums with a bright flame and fragrant odour. It is 

 soluble in alcohol. It is found in the Bovey coal of Devonshire, and 

 also in the brown coal of Wolchow in Moraviaj and near Halle. 

 (Dana, ' Mineralogy.') 



REUSSITE, a Mineral, called also Soda Sulphate of Magnesia. It 

 occurs in flat six-sided prisms, acicular crystals, and mealy efflores- 

 cences. Its colour is snow-white. Fracture conchoidal. Taste saline 

 and bitter. It is found in the vicinity of Seidlitz and of Secdschutz 

 in Bohemia. According to Reuss, it contains Sulphate of Soda, 

 Sulphate of Magnesia, Muriate of Magnesia, and Sulphate of Lime. 



RHAMNA'CE^E, a natural order of Exogenous Plants, remarkable 

 for having a valvate calyx, hooded petals,' opposite to which their 



Rhammu Alatcrnut. 



1, a flower about to expand j 2, a flower cut open to show the position of the 

 .tamens and petals ; 3, a transverse section of a fruit, and seeds. 



