480 MATERIA MEDIC A AND THERAPEUTICS. 



oxygen. The proportion of oxygen to nitrogen in the air may 

 be modified by arrangements for special inhalation, but practi- 

 cally this is seldom attempted, mountain and ocean climates 

 affording us a much more satisfactory supply of pure air. 



(c) The temperature of the air respired may be modified 

 either by selecting particular climates tropical, sub-tropical, 

 temperate, or cold ; by artificial regulation of the atmosphere of 

 the room ventilation, heating, etc. or by arrangements for 

 warming or cooling the ingoing current of air only, by means 

 of so-called "respirators," and by recommending nasal breathing 

 only, or oral breathing only, as the case may be. 



(d) The amount of moisture in the air respired can be altered 

 at pleasure, whether by residence in a dry climate or in a moist 

 climate, or by varying the amount of watery vapour in the air 

 of the room, or in the individual inspiratory draughts, by 

 means of steam kettles, hot- water inhalations, etc. 



(e) Lastly, the pressure of the air is completely under our 

 command ; and this again either by means of climate (elevated 

 mountain residence), or by local artificial arrangements such as 

 the air-bath and pneumatic apparatus. The compressed air-bath, 

 at a pressure of | to J of an atmosphere above the normal, 

 increases the amount of oxygen admitted into the blood, as well 

 as the vital capacity and the size of the lungs, whilst it renders 

 respiration less frequent and more easy. A rarefied atmos- 

 phere is never given as a bath ; on elevated mountains it in- 

 creases the depth and frequency of respiration and the vas- 

 cularity of the lungs, so that there is a tendency to haemorrhage 

 from the alveoli. The pneumatic apparatus, a small gasometer, 

 admits air under artificial pressure to the respiratory passages 

 only, the patient breathing into, or out of, a valved tube con- 

 nected therewith. Inspiration of air compressed by about ^ 

 atmosphere increases the amount of air entering the chest, and 

 eventually the vital capacity, the size of the chest, and 

 the respiratory force, whilst it diminishes the vascularity of the 

 lungs and raises the arterial pressure. The other methods of 

 aerotherapeutics do not require mention here. 



2. The Red Corpuscle. The red corpuscle as the great medium 

 of external and internal respiration, as well as the prime mover 

 of the respiratory centre, is an important agent through which 

 the respiratory activity may be modified by food, drugs, and all 

 the ordinary natural influences, studied in chapter viii. 



3. The Circulation. The corpuscles must be circulated by 

 the heart and vessels, and any effect that we may produce upon 

 these will greatly modify the respiratory functions. The phar- 

 macodynamics of the circulation are discussed in the preceding 

 chapter. 



