634 PRINCIPLES OF GENERAL PHYSIOLOGY 



Scott's experiments (1908) showed that the increased respiratory activity 

 produced by inhalation of carbon dioxide differs in form when the vagi are cut 

 from that when they are intact. In the former case the respirations are increased 

 in depth, without increase in rate, whereas there is an increase in both rate and 

 depth when the vagi are intact. It would appear, then, that the inspirations 

 excited by carbon dioxide in the normal state are cut short by the vagi 

 inhibiting the discharge of the centre ; collapse of the lungs follows rapidly, the 

 inhibition ceases, and the centre is again accessible to excitation by carbon 

 dioxide. In this way we have the advantage of an increased rate in addition 

 to the increased depth. It is interesting that the excitatory effect of carbon 

 dioxide does not cause the centre to discharge more frequently, but with 

 increased strength of discharge. The function of the nervous regulation is thus 

 to moderate the discharge, which tends to be "all or none," in the absence of 

 inhibitory impulses. 



Apncea. Since the stimulus to the respiratory centre depends on the tension 

 of carbon dioxide in the alveolar air, it is plain that a diminution of this tension 

 causes cessation of respiratory movements. This is true apnoea. Considerable 

 discussion took place at one time as to whether a summation of the inhibitory 

 vagus impulses, described in the preceding paragraph, could produce stoppage of 

 respiration. Campbell, Douglas, Haldane, and Hobson (1913) have shown that 

 no apmea can be produced, at least in man, unless the alveolar carbon dioxide 

 tension is reduced. 



EFFECTS OF WANT OF OXYGEN 



Some aspects of this question have been referred to, incidentally, in previous 

 pages. A few words may be added here with respect to "mountain sickness." 

 In a low atmospheric pressure, not only is the oxygen tension below normal, 

 but the alveolar carbon dioxide is also naturally at diminished pressure. Con- 

 sequently, the stimulus to the respiratory centre is absent or very weak, although 

 increased supply of air is necessary. The organism suffers, therefore, from 

 want of oxygen. The symptoms observed on Pike's Peak are described thus by 

 Douglas, Haldane, Henderson, and Schneider (1913, p. 308): constant blueness 

 of lips and face, loss of appetite, nausea and vomiting, intestinal disturbance, 

 headache, sometimes fainting, periodic breathing, and great hypernoea on exertion. 

 Difficulty in mental effort is also experienced. All of these symptoms are such 

 as are produced by want of oxygen. The view of Mosso that "acapnia" or 

 diminution of carbon dioxide is the directly responsible factor can no longer 

 be held (see especially the book by Zuntz, Loewy, Miiller, and Caspari, 1906). 

 The symptoms are almost identical with those of carbon monoxide poisoning, 

 " which have been shown to be due to want of oxygen and to nothing else." 

 The psychical disturbances are often like those of alcoholic intoxication ; unreason- 

 able behaviour on the part of visitors required the presence of a deputy sheriff on 

 Pike's Peak. Perhaps unreasonable people met with under ordinary circumstances 

 are really suffering from want of oxygen. 



The first proof that the symptoms and dangers of low barometric pressure 

 depend on diminished oxygen pressure, and consequent insufficient oxygen content 

 in the blood, was given by Paul Bert (1878). 



In acclimatisation, the acidity of the blood due to non-volatile acids is 

 increased, so that the respiratory centre becomes properly excited, although the 

 alveolar carbon dioxide tension is low. 



It will be obvious that the danger from lack of oxygen is much greater in 

 balloon ascents, where no time for acclimatisation is given. The tragic ascent 

 of Tissandier with two companions in 1875 will be remembered (see Paul 

 Bert, 1878, p. 1063). Some of the words used by Tissandier are worth quoting, 

 as typical of the state of oxygen deficiency. " At about 7,500 m. (3UO mm. 

 barometric pressure) the condition of torpor which comes over one is extra- 

 ordinary. There is no suffering one rises and is glad to be rising. This state 

 of exhilaration continues to fche last moment, and immediately precedes loss of 



