RESPIRATION. 



325 



in a similar manner to the next ring, and so on 

 throughout the series, the posterior two-thirds 

 of each ring being embraced by the following, 

 so that of the three prominent rings that 

 project from each piece the anterior only is 

 visible, the two posterior being contained in 

 the next ring, with the exception of the ulti- 

 mate one. 



The two last rings of each piece thus en- 

 closed in the two first of the succeeding 

 retain it in its place ; but as the diameter of 

 the former is less than that of the latter, each 

 piece is quite loose and plays freely about 

 upon that which it envelopes. None, except 

 the first, are connected with the skin of the 

 animal by any muscle, nerve, or vessel. It is, 

 therefore, merely an external appendage, 

 moved, as any foreign body would be, when 

 the end of the tail is agitated. 



The pieces of the organ are formed suc- 

 cessively on the skin of the tail, receiving 

 from it the materials necessary for its de- 

 velopment, and adhering to it until its growth 

 is complete. A second piece, entirely similar 

 to the first, is formed under it, and detaches 

 it from the end of the tail. It is pushed 

 backwards, leaving between its edge and the 

 skin of the tail an interval occupied by the 

 first ring of the new piece, of which the 

 second and third rings are covered by the 

 first piece. The latter is retained by this 

 connexion, but plays freely round the first 

 piece. A third piece is formed under the 

 second, as that was under the first ; pushing 

 the second backwards, but retaining it by its 

 two posterior rings being included in the 

 cavity of the second piece. 



If the vertebras of the tail continue of 

 uniform diameter, all the pieces will be of the 

 same size, and the rattle, consequently, is of 

 one breadth throughout. On the contrary, 

 if the vertebrae grow while the rattle is being 

 formed, the pieces increase in size, and thus 

 the rattle tapers to its end. 



It is evident from the preceding description 

 that one piece only can be formed at each 

 partial moulting of the end of the tail ; but as 

 we do not know whether these moultings 

 coincide with the general separation of the 

 epidermis from the body, nor the period of 

 their recurrence, the number of pieces not 

 only affords no proof of specific difference, 

 but also indicates nothing about the age of 

 the animal.* 



Musk-gland of the Crocodile. In crocodiles 

 there is a peculiar gland lying under the skin 

 of the lower jaw, on each side about its 

 middle. It is small, of a homogeneous whitish 

 tissue, and is covered by a tendinous sheath. 

 It secretes an unctuous blackish-grey fluid, 

 smelling most strongly of musk, which accu- 

 mulates in a small bag that opens externally 

 by a wide orifice. 



Anal glands have also been observed in the 

 crocodile and alligator, as well as in several 

 serpents: they are of considerable size in 

 female colubers, and are situated under the 



* Lacepede, Hist. Nat. des Serpens. 



tail, behind the cloaca, near the part occupied 

 by the penis of the males. They contain a 

 thin yellow substance of a very peculiar 

 odour. 



Bojanus (Lud. Hen.), Anatome Testudinis Euro- 

 peas. Fol. Viln. 181921. Mohring (C. A.), 

 Diss. inaug. zoot. sistens Descriptionem Trionichos 

 ^Egyptiaci osteologicam. 4to. Berol. 1825. Tiede- 

 mann (F.), Anatomie und Naturgeschichte des 

 Drachens. 3 Kpfn. 4to. Ntirenb. Tyson (Ed. 

 M. D.), Anatomy of the Kattlesnake. 4to. Lond. 

 1751. Hellman (Aug.), Ueber den Tastsinn der 

 Schlangen. 12mo. Getting. Cloquet, Memoire 

 sur 1'Existence et la Disposition des Voies lacrymales 

 dans les Serpens. 4to. Paris, 1821. Cuvier, Re- 

 cherches sur les Ossemens fossiles. 4to. Paris, 

 182124. Home (Sir Everard), Lectures on 

 Comp. Anat. 4to. Lond. 1814 28. Sommering 

 (Detmar. Guil.), De Oculorum Hominis Animalium- 

 que Sectione horizontale Commentatio. Fol. Getting. 

 1818. Brandt (J. F.) und Ratzburg (I. F. C.), Dar- 

 stellung und Beschreibung der Artzneygewachse, 

 welche in die neue Preussische Pharmacopae auf- 

 genommen sind. Cams, Lehrbuch der vergleichen- 

 den Zootomie. 1834. Owen, Odontography. 

 Wagner, Prodromus. Fol. Cuvier, Anatomie 

 Comparee. Last edition. 8 vols. 8vo. Paris, 1840. 

 Schlegel, Essai sur la Physiognomic des Serpens. 

 Amst. 1837. Meckel, Syst. der vergleichenden 

 Anatomie. Perault, Mem. de 1'Acad. des Sciences, 

 torn. iii. 



(T. Rymer Jones.) 



RESPIRATION (Germ. Athmung). Be- 

 fore the nutritious juices of organized bodies 

 can be properly elaborated and rendered fit for 

 maintaining the vitality of the tissues through 

 which they move, it is indispensable that certain 

 chemical changes take place between them and 

 the atmospheric air. All organized bodies, 

 therefore, vegetable as well as animal, require a 

 supply of atmospheric air for the continuance 

 of life, and the amount of this is proportionate 

 to the number and energy of their vital 

 actions. These chemical changes between 

 the nutritious juices of organized bodies and 

 the atmospheric air constitute the important 

 function of Respiration. 



In studying the chemical actions that occur 

 in respiration in different organized bodies, it 

 is necessary to keep in mind the constitution 

 of the atmospheric air, both in its free state 

 and when dissolved in water. The atmo- 

 spheric air, in its free state, is, as is well 

 known, chiefly composed of nitrogen and oxy- 

 gen, in the proportion of about 21 parts of 

 oxygen to 79 of nitrogen by volume ; or by 

 weight, in the proportion of 23' 1 of oxygen to 

 76'9 of nitrogen. Dumas and Boussingault, 

 in their accurate experiments*, found the 

 average proportion of these gases to be, by 

 volume, 20'81 of oxygen, and 79'19 of nitro- 

 gen f ; or by weight, 23'01 of oxygen, and 

 76'99 of nitrogen. The quantity of carbonic 

 acid gas in the atmospheric air is very much 

 smaller than that of the oxygen and nitrogen. 

 Theod. De Saussure , in his experiments, 



* Annales de Chimie et de Physique, troisieme 

 serie, torn. iii. p. 257. 1841. 



f Or, what would be sufficiently accurate, 20-8 

 oxygen and 79*2 nitrogen. 



| Annales de Chimie et de Physique, torn, xxxviii. 

 p. 411. 1828. 



Y 3 



