RESPIRATION 



rapidity, extra muscles are called into play, the 

 expiratory movements are e-pecially marked ; then 

 all the muscles that can possibly aid in expiration 

 are used, the excitement spreads to nearly all the 

 muscles of the body, and convulsions set in ; these 

 violent efforts exhaust the Ixxly. (3) A stage of 

 ipiiet, due to exhaustion, occurs ; a few long drawn 

 in-piratory gasps are made, these die out; the 

 whole Iwldy is convulsively stretched out, and 

 death intervenes. When the trachea of a dog is 

 artificially closed these events run their course in 

 from four to five minutes; the convulsions appear 

 at the end of the first minute, and cease suddenly 

 within the second minute. In drowning death is 

 often hastened by the entrance of water into the 

 lungs. The time at which death from drowning 

 occurs varies with the state of the animal at the 

 time of the occurrence. Young animals e.g. a 

 puppy -in which the respiratory changes are h-s 

 active than in adults, may survive an immersion 

 of fifty minutes; but a full-grown dog rarely 

 vers after having been U minute under water. 

 I'or man, see below, p. 667. My training, as in 

 the case of divers, the respiratory centre may l>e 

 accustomed to lear the scarcity of oxygen for 

 much longer than it can normally. 



We next consider the effects of changes in the 

 partial pressures of the gases of the atmosphere, 

 the total pre nte remaining more or less un- 

 changed. Lessened partial pressure of oxi/i/cii, as 

 already noted, results in asphyxia. I in-rawed 

 partial pressure of oxygen results in the pheno- 

 menon known as apneea. After several very deep 

 inspirations the state known as njinoea ocelli's, and 

 it i- c:tsy to hold the breath for a longer time than 

 ii-ual. 'The usual explanation of this has been 

 that the oxygenation of the blood is so complete 

 that there i- enough to last some time, and the 

 centre is not stimulated by its absence or by the 

 pp'-ence of the reducing stuff in the Mood. Later 

 authorities regard the cessation of respiratory move- 

 ment- which occur when oxygen is rapidly forced 

 into the lungs by rapidly succeeding respiratory 

 movement- as due to fatigue of the respiratory 

 apparatus. Increanal partial pressure of carbonic 

 acui tends to the accumulation of carbonic acid in 

 the blood, ultimately producing a stale of narcosis 

 without convulsions. l)r,-mi.ii-il partial pressure of 

 carbonic acid results merely in the carliimic acid of 

 the Mood being able to leave the blood with greater 

 readiness. Alterations in the partial pressure of 

 nitrogen have no effect. Ozonr, instead of making 

 the Id. Kid more arterial, as one might expert, makes 

 it more venous, and cause- irritation of the respira- 

 tory passages. Carbonic n.riilr combines with the 

 hemoglobin with more avidity than oxygen ; con- 

 sequently it interferes with due respiration. Sul- 

 iiliuri'ttrd In/ilroyen, acting as a reducing agent, 

 has ultimately the s-ime effect. \ilroiu oxide 

 ( laughing gas) produce- narcosis, and is used as an. 

 anesthetic. Some gases /ii/i/m>/'-n, iinn-.i/i-ifn-i, 



and other neutral gases have i Meet. Some 



rhl'irinr, iniiiiiniiiii, &C, cause spasm of the glottis, 

 and so cannot be breathed. 



Another point to attend to is the effect of varia- 

 tions in external pressure, the proportional com- 

 position of the atmosphere remaining unchanged. 

 Sudden and great diminution of pressure will . 

 fatal convulsion-, due to the sudden liberation of 

 bubbles of the ga-e-of the blood within the vessels; 

 these plug up the smaller vessel-, and affect the 

 working of the valves of the heart, and cau-e 

 asphyxia. If the pressure lie gradually iliininixhed, 

 as ill ascending a mountain, no effect even at con- 

 siderable height- i- e\|K'iienced lieyond a feeling of 



'dislre ' often accompanied by Id ling at the 



nose. This is due to a derangement of the vascular 

 system, the walls being constructed to meet a 



certain external pressure. If only the respiratory 

 interchange of g i-c- wcie concerned, the total 

 external pressure might lie reduced from 760 mm 

 to 300 nun., corre-|N>ndiiig to a partial pressure of 

 11 of 7ti nun., and to an altitude of 17.(HH 

 before the combination of oxygen wilh 

 hemoglobin, at the temperature of the bloo.l. 

 would lie .seriously affected. In various part- of 

 the world there are people living at an altitude of 

 11,000 feet. If the pressure be still furthi-i redm .1 

 a-ph\ xia occurs, but it is not quite the same 

 asphyxia a- that which re-nlts from absem 

 oxygen ; the characteristic convulsions are oflcn 

 absent, while a rapid onset of feebleness amount- 

 ing almo-t In paralysis occurs. Increaseof prc ure 

 up to a pressure of several atmospheres is followed 

 only b\ symptoms of drowsiness, due probably In 

 increased pressure n|x>n the whole organism lather 

 than to a direct derangement of respiration. At a 

 pressure of fifteen atmospheres, which conesponds 

 to a partial pressure ol oxygen of ihice atmo- 

 spheres, the animal ilics of a-phyxia with convul- 

 sions as though from n deficiency of oxygen. The 

 production of carbonic acid is diminished with 

 increase of prcs-mc i.e. the oxidations of the 

 whole body are le-scned. At a certain (mint ih .- 

 oxidations cease, and the animal dies. All living 

 tilings are killed by a too great pressure of oxygen. 

 The oxidations of some other substances e.g. 

 phosphorus are analogous ; at a certain pressure 

 they will not burn. 



The effect of variations in temperature must not 

 be overlooked. My variations in temperature we 

 mean of course variations in the temperature of 

 the body and of the blood, anil not merely varia- 

 tions in the temperature of the surrounding 

 medium, for these have normally, in warm-blooded 

 animals (the temperature of cold-blooded animals 

 varies with that of the surrounding medium), 

 no effect upon the temperature of the body, owing 

 to the regulating mechanism afforded by the 

 vessels of the skin and vaso-motor system (see 

 <'n:ri I.ATION ). The temperature of an K-kinm 

 is nearly the same as that of an African : and in a 

 Turkish bath the temperature only rises a veiy 

 little. In cold -blooded animals the oxidative and 

 chemical processes of the body decrease with a 

 lowered temperature, and increase with increase of 

 temperature; but the reverse is the case with 

 warm-blooded animals, for the temperature of the 

 body in an atmosphere of low temperature is partly 

 kept up by increased oxidation ; out in fever i.e. 

 when the temperature of the blood is actually 

 raised the chemical activity of the body of a 

 warm blooded animal rises. Such an animal dies 

 when the temperature of its blood rises to ! 

 or 50' ('.. a mammal at 4.T ( '. , and a bird at 50 C. 

 Death is due to the fact that when the tcmpeta 

 line rises tu this point the partial pressure of (he 

 oxygen of the air is no longer sufficient to main- 

 tain the combination of oxygen with hemoglobin. 



Tl retically a higher temperature n.ighl lie snr 



vived if the external partial pressure of oxygen 

 were proportionally increased. 



IN SKI: on Tisst'K KKSPIHATION. We now come 

 to the la-l and most interesting part of our subject 

 the manner in which the oxygen of the blood 

 enleis the tissues-, the use made of this oxygen by 

 the cells of the I issues finally resulting in the for- 

 mation of carbonic acid, and the manner in which 

 this carlMinic acid leaves the tissues and enters the 

 Mood. The term ' inner respiration ' is by some 

 wriieis restricted to the interchange of the gases 

 between the tissues and the blood ; but it is 

 usual and more convenient to include in that term 

 what is known of the uses made of the gases 

 by the cells. We have spoken with confidence 

 of this respiratory action of all the cells of the 



