RESPIRATION. 209 



larger. These are called Traubes or Traube- Her ing's curves. They con- 

 tinue whilst the blood-pressure continues to rise, and only cease when the 

 vaso-motor centre and the heart are exhausted, when the pressure speedily 

 falls. These .curves must be dependent upon the vaso-motor centre, as 

 the mechanical effects of respiration have been eliminated by the poison 

 and by the cessation of artificial respiration, and the effect of the cardio- 

 inhibitory centre be the division of the vagi. It may be presumed there- 

 fore that the vaso-motor centre, as well as the cardio-inhibitory, must be 

 considered to take part with the mechanical changes of inspiration and 

 expiration in producing the so-called respiratory undulations of blood- 

 pressure. 



Cheyne- Stokes' s breathing. This is a rhythmical irregularity in respi- 

 rations which has been observed in various diseases, and is especially con- 

 nected with fatty degeneration of the heart. Respirations occur in groups, 

 at the beginning of each group the inspirations are very shallow, but each 

 successive breath is deeper than the preceding until a climax is reached, 

 then comes in a prolonged sighing expiration, succeeded by a pause, after 

 which the next group begins. 



AP^CE A. D YSP:NXE A. ASPHYXIA. 



As blood which contains a normal proportion of oxygen excites the 

 respiratory centre (p. 204), and as the excitement and consequent respir- 

 atory muscular movements are greater (dyspnoea) in proportion to the 

 deficiency of this gas, so an abnormally large proportion of oxygen in the 

 blood leads to diminished breathing movements, and, if the proportion be 

 large enough, to their temporary cessation. This condition of absence of 

 breathing is termed apncea, 1 and it can be demonstrated, in one of the 

 lower animals, by performing artificial respiration to the extent of satura- 

 ting the blood with oxygen. 



When, on the other hand, the respiration is stopped, by, e.g., 

 interference with the passage of air to the lungs, or by supplying air 

 devoid of oxygen, a condition ensues, which passes rapidly from the state 

 of dyspnoea (difficult breathing) to what is termed asphyxia; and the 

 latter quickly ends in death. 



The ways by which this condition of asphyxia may be produced are 

 very numerous; as, for example, by the prevention of the due entry of 

 oxygen into the blood, either by direct obstruction of the trachea or other 

 part of the respiratory passages, or by introducing instead of ordinary air 

 a gas devoid of oxygen, or, again, by interference with the due inter- 

 change of gases between the air and the blood. 



Symptoms of Asphyxia. The most evident symptoms of asphyxia 

 or suffocation are well known. Violent action of the respiratory muscles 



1 This term has been, unfortunately, often applied to conditions of dyspncea or 

 asphyxia; but the modern application of the term, as in the text, is the more convenient. 

 VOL. I. 14. 



