GENERAL STRUCTURE OF THE RESPIRATORY ORGANS. 375 



ing the movements of the tongue; to the inferior nucleus of the facial, ivgu- 

 lating the movements of the lips ; and to the nucleus from which the cardiac 

 branches of the spinal accessory and pneumogastric nerves arise. In the 

 disease known as glosso-labio-laryngeal paralysis these centres are affected 

 successively, the tongue being first affected ; then the muscles of the palate; 

 then the orbicularis oris, whilst the fatal termination of the disease is pre- 

 ceded by attacks of suffocation. 



294. The respiratory centres are capable of being excited to action in two 

 ways: directly, by changes in the quality of the blood traversing their cap- 

 illaries; and reflectorially, by excitation of the sentient extremities of the 

 vagi and many other nerves. The condition of the blood by which they are 

 directly excited, consists in the diminution of Oxygen and the accumulation 

 in it of Carbonic acid, or possibly of other products of the disintegration of 

 the tissues. Nasse maintains 1 that it is not the diminution of oxygen which 

 constitutes the stimulus, but that such diminution causes the Central ganglia 

 to respond more readily to the ordinary and a fortiori to any extraordinary 

 quantity of Carbonic acid in the blood ; on the contrary, their irritability is 

 lowered' when the proportion of oxygen in the blood circulating through 

 them is increased. In proportion as these alterations in the relations of the 

 gases become more pronounced, the "besoin de respirer" is rendered more 

 intense, and the respiratory movements become more and more energetic till 

 Dyspnoea is established, which gradually passes into Asphyxia, in which the 

 centres are paralyzed. If, on the other hand, the proportion of oxygen in 

 the blood is rendered high either by the active performance of artificial 

 respiration, or by the inhalation of oxygen/ whilst at the same time, no 

 obstacle is presented to the elimination of carbonic acid gas, the activity of 

 the ganglia is lessened, the respiratory movements become reduced in num- 

 ber and extent, and the animal passes into the state of Apnwa. 3 Between 

 these two states is that which exists in the normal aeration of the blood, 

 and results in ordinary breathing, or Eupncea. Dyspnoea from deficiency 

 of oxygen can be produced by the inhalation of Nitrogen or Hydrogen ; in 

 such cases Pfliiger has shown, the oxygen is greatly diminished, whilst the 

 carbonic acid is not materially increased, or may be even diminished. 4 

 Dyspncea from excess of carbonic acid can be induced by making the animal 

 breathe air surcharged with that gas, or by preventing its elimination from 

 the system. Traube 5 produced dyspnoea by making an animal breathe a 

 mixture of 28 per cent, of carbonic acid gas, 32 per cent, of oxygen, and 40 

 per cent, of nitrogen. 6 Dyspnoea produced by such gases as carbonic oxide 

 and nitrous oxide is due apparently to these gases withdrawing oxygen 

 from the blood, whilst phosphuretted, arseuiuretted, and sulphuretted hy- 

 drogen reduce the haemoglobin, and after first exciting rapidly paralyze 

 the respiratory centres. Hydrocyanic and hydrochloric acid gases, chlorine, 

 sulphurous acid, and some other gases seem both to act destructively on the 

 blood, and to destroy the functional activity of the vagal nuclei. 



1 Centralblatt, 1870, p. 275. 



2 See the experiments of Czermak, Centralblatt, Jan. 3d, 1866; Pfliiger, Pfluger's 

 Archiv, 1868, p. 61; Schwarz, Beitriige. 



3 Evvald, Pfluger's Archiv, 1873, p. 575; Zur Kenntniss der Apncea. 



4 See Pfluger's Es.-^ay in Band i, of his Archiv, 1868. 



5 Allgem. Med. Centralblatt, 1868, Nos. 38 and 39. See also Thiry, Rec. des 

 Travaux de la Soc. Med. Allemande de Paris, 1865; and Dohraen, Unters. aus dem 

 Physiol. Lab. zu Bonn, 1865, p. 83. 



6 M. Bert (Seance de la Soc.de Biologie, Feb. 3d, 1872, Rev. Scient., 2" Ser., 

 i Annee, No. 37, 1872, p. 882) has shown that the barometric pressure to which the 

 animal is exposed is of great importance in such experiments in consequence of its 

 eflects on the diffusion of the gases. 



