356 



RESPIRATION. 



The experiments on the effects of dimi- 

 nished frequency of the respirations in re- 

 ducing the amount of carbonic acid gas 

 evolved from the blood in a given time, are in 

 accordance with observations made on the 

 state of the blood and its circulation, when 

 this condition has been induced in man or in 

 the other warm-blooded animals. A diminu- 

 tion in the frequency of the respiratory move- 

 ments occasionally occurs to a notable extent 

 in the course of some diseases, and this de- 

 serves the careful attention of the practitioner, 

 as it is likely to lead to very serious conse- 

 quences.* 



The greater length of time that the respi- 

 rations may be suspended without inducing 

 insensibility, when a deep expiration followed 

 by a deep inspiration has immediately pre- 

 ceded, affords additional illustration of the 

 procedure which a person ought to adopt 

 when he wishes to suspend, during diving, 

 &c., the respirations for the longest period 

 consistent with his safety. The manner and 

 the order in which the vital actions are 

 brought to a stand when the chemical changes 

 between the blood and the atmospheric air 

 are arrested, have been discussed under the 

 article AsFHYxiA.f 



six per cent, by volume of carbonic acid gas cannot 

 exist in the air without danger to life, and that less 

 than half this amount will soon be fatal, when it is 

 formed at the expense of the oxygen of the air." 

 (Opus cit. p. 54.) Leblanc ascertained that an ad- 

 dition of 3 or 4 per cent, by weight of carbonic acid 

 formed by the combustion of charcoal, and at the 

 expense of the oxygen of the air respired, proved 

 instantly fatal to dogs, while it required the addition 

 of 30 or 40 per cent, of pure carbonic acid gas to the 

 atmospheric air to produce the same effect. The 

 great activity of air deteriorated by the burning of 

 charcoal in producing asphyxia, Leblanc attributes 

 to the presence of carbonic oxide. He states that 

 birds placed in air containing one per cent, of this 

 gas, die in two minutes (Opus cit. pp. 240 and 245). 

 Legallois (Annales de Chimie et de Physique, torn, 

 iv. p. 113. 1817) had previously performed experi- 

 ments, from which it may be inferred that an addi- 

 tion of somewhat more than 20 per cent, of carbonic 

 acid to the atmospheric air, is sufficient to bring 

 the evolution of carbonic acid from the blood in the 

 lungs to a stand in the warm-blooded animals, and 

 that, when the percentage of carbonic acid in the 

 inspired air is increased to above 30, part of this gas 

 is absorbed by the blood. 



* We have given some illustrations of this in 

 pointing out the manner in which division of the 

 vagi nerves causes death. (Edinburgh Medical and 

 Surgical Journal, vol. li. p. 298 to 302. 1839.) 



t We have published a series of experiments 

 (Edinburgh Medical and Surgical Journal, vol. Iv. 

 1841) which go to support the account given of the 

 manner in which the vital actions are arrested in 

 asphyxia in the article referred to. In this we ob- 

 tained satisfactory proof of the opinion of Bichat]upon 

 the effects of the venous blood in suspending the sen- 

 sorial functions. In an excellent experimental essay 

 on this subject, published subsequently to our essay 

 (Edinburgh Med. and Surg. Journal, vol. Ixiii. 1845), 

 the author maintains, in opposition to the doctrine 

 laid down in the article ASPHYXIA, " that the flow of 

 blood through the lungs is arrested in consequence 

 of the venous blood acting as an excitant to the 

 minute branches of the pulmonary veins and causing 

 their contraction." In our experiments we found 

 that, when the suspension of the respiration had been 



Experiments have been made by Nysten*, 

 by Mr. Macgregor-j-, Dr. MalcolmJ, and by 

 Hannover , upon the quantity of carbonic 

 acid gas evolved from the lungs in some 

 diseases, but these have not yet been carried 

 sufficiently far to furnish us with any practical 

 or theoretical conclusions of importance. 



Differences between arterial and venous blood. 

 A knowledge of the chemical and physical 

 differences between arterial and venous blood, 

 or, in other words, between the blood imme- 

 diately before and immediately after it has 

 passed through the lungs and been subjected 

 to the action of the atmospheric air, consti- 

 tutes part of the data requisite for discussing 

 the Theory of Respiration. Although many 

 able chemists and physiologists have of late 

 years directed their attention to this subject, 

 yet, from its inherent difficulties, much discre- 

 pancy of observation and conflicting evidence 

 still require to be cleared up and reconciled. 

 Most, if not all, of the comparative analyses 

 of the venous and arterial blood hitherto pub- 

 lished are of considerably less value for our 

 present purpose than they may at first appear, 

 since only those of the venous blood flowing 

 from the right side of the heart, and the arte- 

 rial blood flowing from the left side of the 

 heart or along the arteries, ought properly to 

 be taken into account. The blood returning 

 along the veins of the abdominal viscera, and 

 entering the heart by the cava inferior, differs 

 in composition from that entering the heart by 

 the cava superior, for, independently of other 

 reasons, a quantity of water and certain sub- 

 stances taken into the stomach are absorbed 

 by the mesenteric and gastric veins. The 

 composition of the blood in the large veins at 

 the lower and lateral parts of the neck must 

 also be somewhat affected by the lymph and 

 chyle poured into that portion of the venous 

 system. The analyses of venous and arterial 

 blood taken at the same time from the carotid 

 artery and the jugular vein, the plan most 

 generally followed in these researches, are 

 better fitted for throwing light upon the 

 changes the blood undergoes in the perform- 



carried so far as to arrest the flow of blood through 

 the lungs, the admission of atmospheric air was in- 

 stantaneously followed by the renewal of the passage 

 of the blood to the left side of the heart, a fact in- 

 compatible with this opinion, seeing that the blood- 

 vessels are endowed with that kind only of con- 

 tractility which manifests itself by slow contractions 

 and equally slow relaxations. 



* Recherches de Physiologic et de Chimie Patho- 

 logique. Seconde section. 1811. 



f Edinburgh Monthly Journal of Medical Science, 

 vol. iii. p. 1. 1843. 



J Transactions of British Scientific Association, 

 for 1840, p. 87. 



De Quantitate relativa et absoluta Acidi Car- 

 bonici ab Homine sano et aegroto exhalati. 1845. 

 Hannover, in his experiments, employed the appa- 

 ratus of Scharling, and was enabled to ascertain the 

 absolute quantity of carbonic acid evolved from the 

 body ; while the other experimenters ascertained 

 its percentage only. There can be no doubt that the 

 plan adopted by Hannover is the one which ought 

 to be followed. * 



