RESPIRATION. 



than uiual. The fact formerly known, that the confump- 

 tion of oxygen is influenced by the food and the ftate oi di- 

 geftion, was confirmed and more accurately deuionftrated 

 by Lavoifier and Seguin. They found, that during digef- 

 tion the conlumption of oxygen was increafed to iSoo or 

 1900 cubic inches in an hour. Exercife, too, incn 

 proportion confumed. It is ilated that Seguin, m con- 

 tinuing the exercife of railing a weight of 15. pounds to a 

 height of 613 feet during a quarter of an hour, confumed 

 800 cubic inches, which is at the rate of 3200 in an hour ; 

 and the fame exercife, made during digeftion, occafioned a 

 confumption equal to 4600. 



Notwithstanding, however, fays Mr. Ellis, the neceffity 

 of oxygen gas to the continuance of refpiratian, and the 

 great quantity of it that is thus dail' c umed, inany 

 facts tend to prove, that, by the very conftitution of that 

 function, a neeellary limit is placed to its confumption : and 

 that this limit is determined, not by the purity of the air 

 employed, but by fame circumftances inherent in the animal 

 fyltetn. It has been found, that the growth of vegetables 

 is retarded by a great fuperabundance cf oxygen 1 Ellis's 

 Inquiry, ^ 14 40.) ; and that, although infects will live a 

 confiderable time in this gas, yet their breathing becomes 

 opprefiive, and they die (ibid. § 53.) long before the whole 

 of it is confumed. There can be little doubt but that the 

 other dalles of inferior animals would, under the fame cir- 

 cumftances, fuller in the fame manner. In the experiment 

 alfo made by Lavoifier on the guinea pig, already doienbed, 

 the animal is faid to have breathed with much difficulty, 

 although not more than one-fifth of the oxygen gas was 

 confumed : but fome experiments of the fame author, at a 

 later period, feem in oppofition to this fact. In comparing 

 together the phenomena of combuftion and refpiration. he 

 obferves, that much more combuflible matter is confumed in 

 a given time in vital air, than in that of the atmofphere, 

 but that the fame circumftance does not hold in refpiration : 

 for whether animals refpire oxygen gas in its pure ftate, or 

 mixed with a proportion, more or lefs confiderable, of nitro- 

 gen gas, the quantity of oxygen which they confume is 

 always the fame. If a guinea pig, he adds, be kept for 

 feveral days in oxygen gas, or in a mixture compofed of 

 fifteen parts nitrogen and one of oxygen, preferving con- 

 ftantly thefe proportions, the animal in both cafes continues 

 in his natural ftate : his refpiration and circulation do not 

 fenfibly appear to be either accelerated or retarded : his tem- 

 perature remains the fame, and he has onlv, when the pro- 

 portion of nitrogen gas is too great, a flight difpofition to 

 drowfinefs. Mem. de l'Acad. 1789. 



The refults of Mr. Davy's experience, however, do not 

 correfpond with thefe conclufions of Lavoifier. He intro- 

 duced a moufe into ajar containing an atmofphere compofed 

 of 1 0.5 cubic inches of oxygen, and three inches of nitrogen 

 gas. In half an hour the animal appeared to fuffer much, 

 and, in about an hour, lay down on his fide, as if dying : 

 in an hour and a quarter he was withdrawn from the jar 

 alive, but motionlefs. The refidual air, on being analyfed, 

 was found to have loft only 2.1 cubic inches of its oxygen 

 gas, and confequently 8.4 inches of that gas A. ill remained. 

 Another moufe, which was put at the fame time into a jar 

 containing 15.5 cubic inches of atmofpherie air, was taken 

 out through the mercury alive, but unable to Hand, in 50 

 minutes: and on analyfing the refidual air, 2.7 cubic 

 inches of its oxygen were confumed. Hence it appears, 

 that the moufe in atmofplu rie air confumed nearly o hird 

 more of oxygen in 50 minutes, than the other moufe did 

 in an hour and a quarter, when placed in a jar con: 

 fo large a portion of oxygen. (Refearches, p. 443-) 



The refults of thefe ex;. are corrobo- 



rated by thofe made by Mr. Davy on his own refpiration ; 

 for he found, that he confumed much lefs oxygen gas when 

 he refpired it pure, than when, for the fame length of time, 

 he breathed atmofpherie air; and the quantity of carbonic 

 acid formed in the firft cafe, was but little more than half 

 that obtained by the relpiration, for the Came time, of 

 atmofpherie air. (Ibid. 442.) Meffrs. Allen and Pepys 

 ftate, on the contrary, that when pure oxygen gas is 

 breathed, more of it ia ccnlumedin a given time, and more 

 carbonic acid formed, than in breathing atmotpheric air. 

 The experiments of Davy differ greatly therefore from thofe 

 of Lavoifier as to the effects produced by the refpiration of 

 oxygen on the animal fyftem ; for, while the latter philo- 

 fopher informs us, that this gas may be refpired for many 

 davs without inconvenience, Mr. Davy has Inewn that the 

 animal dies long before the whole of it is confumed. Truil- 

 in£c, therefore, to the accuracy of Mr. Davy's experiments, 

 as in all refpects fupported by analogy, we inter, that an 

 excels of oxygen gas in the air that is breathed, is not 

 fuited to the d, innce of the refpiratory function : 



and, on the other hand, the oppreffive fj which the 



relpration of impure air- occafions, . is the refults of 



Lavoiiicr's experiments, in which nitrogen fuperabounded, 

 equally inltruct us, that a deficiency of this gas is alike un- 

 fuited to it. Confequently, we may conclude, that the atmo- 

 fphere, as it is naturally compofed, is bell adapted to the 

 economy of the animal fyftem ; but that this fyftem is, at the 

 fame time, fo conftituted, as to be able to bear great varia- 

 tions in the compofition of the air without immediate injury 

 to the powers of animal life. 



When, however, this variation proceeds to a certain ex- 

 tent, the air is no longer capable of fupporting vital action ; 

 but different animals, when confined in given volumes of air, 

 poffefs the power of prolonging this action in very different 

 degrees. Thus infects, worms, fillies, and the amphibia, 

 live until all the oxygen gas of the air is nearly or entirely 

 confumed (Ellis's Inquiry, j 53, et feq.) ; while birds die in 

 a given quantity of air before they have confumed two- 

 thirds of its oxygen (ibid. § 84.), and a motile and guinea 

 pig expire when about three-fourths of this gas have difap- 

 peared. Dr. Prieltley obftrved, that if a moufe can ftand 

 the firft fhock of being put into impure air, or has been ha- 

 bituated to it by degrees, he will live a confiderable time in 

 air in which other mice will inltantaneoufly die. (Experi- 

 ments on Air, p. 257.) When, however, death does happen 

 to animals in a given volume of air, it mult arife either froa\ 

 the noxious operation of the nitrogen gas that is always pre- 

 fent, or from that of the carbonic acid, which is formed ; 1 

 or it mull proceed from the deficiency, or total abfence, of 

 oxygen gas. Now, although nitrogen gas do not of itfelf 

 fupport life, yet we have no evidence that it exerts any 

 injurious effects on the animal fyftem. In vegetation, and 

 in the refpiration of the inferior animals, it has been (hewn 

 to br- wholly inactive ; and when, in the experiment of La- 

 voifier, it conftituted 4 ,; t h s of the air employed, a degree 

 of drowfinefs only feems to have been induced by it. That 

 it is entirely paffive, is ftill farther confirmed by an experi- 

 ment of Lavoifier, who found that hydrogen gas, mixed in 

 due proportion with oxygen, would ferve the purpofes of 

 refpiration as well as the air of the atmofphere. We have 

 no proof that nitrogen is able to enter the veflels fo as to 

 produce any direct: operation on the blood, — a:i effect which 

 is ftill farther forbidden by its incapacity of uniting with that 

 fluid. We may therefore conclude, that nitrogen gas, when 

 refpired, neither fuffcrs any change itfelf, nor produces any 

 direct operation on the animal fyftem. 



The 



