328 RESPIRATION. 



movements co-operate in the most powerful manner in the pro- 

 duction of the result; for in every inspiration, so long as the 

 pleural cavities remain closed, the diastolic impletion of the 

 heart is favored by the filling of the venae cavse, and thereby 

 the vigor of the succeeding contractions of the heart is in- 

 creased. This is particularly the case in animals which (like 

 the dog and cat) breathe thoracicalty. 



SECTION VII. APNCEA, DYSPNCEA, AND ASPHYXIA. 



The terms apncea, dyspnoea, and asphyxia, are applied in 

 physiology to the states of functional disorder which are 

 produced by excess and defect of oxygen in the blood, the 

 differences between them being in accordance with a gene- 

 ralization so well established that it may be regarded as a law 

 that the activity of the respiratory movements varies in- 

 versely as their effect on the blood. 



107. Apncea. When the blood is saturated with oxygen, 

 respiratory movements cease, and the animal is said to be in a 

 state of apncea. The fact can be demonstrated with great 

 ease in the rabbit by the ordinary method of artificial respira- 

 tion. If the intervals between the inflations of the lungs 

 are gradually shortened, the inspirator}' movements become 

 shallower ana shallower, and finally cease. The heart con- 

 tinues to beat vigorously and somewhat more frequently than 

 before. The visible mucous membranes present a perfectly 

 natural appearance. The eye closes instantly when the con- 

 junctiva is touched, and the state of the pupil is normal. In 

 short, all the functions excepting the respiratory movements 

 go on as before. 1 



108. Dyspnoea. We have already studied the phenomena 

 of dyspnoea so far as relates to the muscular movements. We 

 have seen that in the rabbit, when the access of air to the cir- 

 culating blood is gradually diminished, other muscles begin to 

 co-operate with the diaphragm in the inspiratory act, in an 

 order which, as a rule, is a follows: Inter costales externi, leva- 

 tores costarum breves, intcrcartilaginei, ycaleni, serrati postici. 

 As external signs of dyspnoea, the drawing down of the larynx 

 in inspiration by the muscles which cover the trachea, and the 

 expansion of the upper part of the chest \>y the intercartilagi- 



1 The fact of apnooa was first demonstrated by Hook, before the 

 Royal Society in October, 1667. His experiment consists in op'ening 

 the chest of a dog, distending the lungs with bellows, and keeping up 

 a constant stream of air through the organ through punctures made in 

 its surface for the purpose. He found that, although "the eyes were 

 all the time very quick, and the heart beating regularly," there were 

 no respiratory movements. The term " apnooa" was first applied to 

 this condition by Rosenthal, in 1864. 



