332 RESPIRATION. 



either inspiratory or associated in their action with inspiration, 

 become relaxed. The inspiratory muscles, on the contrary, act 

 with great vigor. 



111. State of the Circulation in Asphyxia. This may 

 be best studied by actually observing the condition of the heart 

 and great vessels in a narcotized animal, of which the chest has 

 been opened while respiration is maintained artificially. In a 

 perfectly chloralized animal, the heart may be exposed very 

 rapidly, as follows : The integument covering the left side of 

 the chest having been turned back, a series of strong ligatures 

 are passed round* the costal cartilages, close to the left edge of 

 the sternum, in such a way that each ligature enters the thoracic 

 cavity by one intercostal space and passes out by the next; a 

 second set of ligatures are passed in a similar manner round the 

 ribs in a vertical line outside of the praecordia. The ligatures 

 having been tightened, the quadrangular space between them 

 can be cut away without any bleeding. The pericardium having 

 then been opened, the thoracic organs can be perfectly well seen. 

 If now after continuing the artificial respiration till apncea is 

 produced, it is suspended, all the degrees of respiratory activity. 

 viz., apnoea, natural breathing, hyperpnoea, dyspnoea, convul- 

 sion, asphyxia, will be witnessed in the order in which they have 

 been mentioned, and it will be seen that no very obvious change 

 in the condition of the heart and great vessels will occur until 

 the last stage (corresponding to what I have called the second 

 stage of asphyxia) is approached. During the convulsive strug- 

 gle, and particularly towards its close, the heart enlarges to 

 something like the double of its former dimension, this enlarge- 

 ment being due (as the attentive observer will have no difficulty 

 in satisfying himself) to the lengthening of the diastolic inter- 

 val and to the quantity of blood contained in the great veins, 

 which in fact are so distended, that if cut into they spirt like 

 arteries. If at this point air is again injected, the heart begins 

 after a few seconds to contract more rapidly, and in a moment 

 or two, emptying itself of its overcharge of blood, resumes its 

 former size. The effect of these changes on the arterial pres- 

 sure can be best studied in a curarized animal, of which the 

 crural or carotid has been connected with the kymograph. If, 

 in such an animal, artificial respiration is discontinued till the 

 arterial pressure, after first increasing, sinks as low as 20 to 40 

 millimetres, the tracing shows that the diastolic intervals are 

 much lengthened. If then air is injected, the arterial pressure 

 after an interval of 5 or G seconds suddenly rises, while the 

 curve expressing the rise indicates the extreme frequency of 

 the contractions by which the heart empties itself of its con- 

 tents, or rather pumps on the blood contained in the over-full 

 veins to the arterial system. (See fig. 264, in which i indicates 

 the moment of injection of air.) During this effort, the mer- 



