REVIEWS HUMAN PHYSIOLOGY. 251 



the muscular contraction of the circular organic fibres, and are delivered 

 into the larger bronchial tubes, in which difFusion at once takes place 

 with the air just introduced ; as soon as the expiration is completed, 

 relaxation of the muscular fibres occurs, and the passages and air cells 

 dilating both through their own elasticity and the exhaustive efi'ect 

 arising from the simultaneous contraction of other bronchial trees, 

 fresh air is drawn into them : the alternate expulsion and introduction 

 being accomplished by muscular contraction and elasticity ; the differ- 

 ent bronchial trees coming into action at different periods of time, 

 some being contracting while others are dilating." With the first 

 portions of this extract we have no fault to find ; besides the information 

 given, the impression is that the vesicles contain a larger percentage 

 of carbonic acid than the tubes, and these than the trachea — ^just as 

 the trachea has more than the atmosphere without ; it gives the dis- 

 tinct information that the act of inspiration is not instant but consecu- 

 tive — that the pure air does not at once reach the periphery of the air 

 cells, but is diffused into, intermingled with that left after the pre- 

 ceding expiration; but that with each flow and ebb of this tidal 

 current, less charged air penetrates to the utmost bounds of its excur- 

 sion, while a relatively noxious mixture is in turn expelled into the 

 ethereal reservoir without, in each act of inspiration and expiration, 

 the whole volume of the air in the lungs is in movement, and hence 

 the vesicular murmur heard by the ear. But the whole of the deteri- 

 orated air is not expelled, nor is the whole of the oxygen of the 

 inspired air absorbed ; portions of each are being commingled, the one 

 losing carbonic and acquiring oxygen, while the reverse occurs with 

 the other ; and hence the comprehension of the value of a sigh-deep 

 inspiration, in languid or depressed condition, and so, too, the positive 

 luxury of a sneeze, in which- a larger volume than ordinary of vitiated 

 air is expelled and a proportionately large inspiration follows. So, too, 

 we think may be explained the effect of blowing steadily for a short 

 time — a fire, for instance — by which act many persons are made to 

 feel giddy — a cerebral effect, doubtless ; during the act of blowing 

 in this manner, it is not air from the lungs that is expelled, but air 

 drawn in through the nostrils ; thus then expiration, properly speak- 

 ing, is not efficiently carried on, accumulation of carbonic acid pro 

 tanto occurs, begins to influence the system, the first manifestation of 

 which is that of giddiness. A part of this eff'ect may be and is, we 

 believe, usually wholly attributed to the pressure on the jugular veins, 

 retarding during the act the return of the blood from the brain ; but 

 that this cannot be the sole cause is shown by the fact that exertion. 



