ON RESPIRATION 517 



Respiration, therefore, becomes a function of equal 

 physiological importance with alimentation, and of even 

 greater immediate imminence in the economy of life, 

 since its rhythmic continuity is essential, every few seconds 

 of time, to meet the demands of the blood streams as 

 they circulate through the capillary elements of the 

 respiratory mucosa that mucosa embracing the linings 

 of the nasal passages, the pneumatic spaces of the head 

 and face, or the cephalic lungs, the larynx, trachea, 

 bronchi, bronchioles, and pulmonary vesicles. 



It must be borne in mind that the whole extent of the 

 submucous capillary blood vasculature of the air-passages 

 partakes in the performance, to a greater or lesser extent, 

 in accordance with the thickness or thinness of the epi- 

 thelium, in the phenomena of oxygenation or arterialisa- 

 tion of the blood, and that the "cephalic lungs" 

 especially, from the diaphanous condition of their lining 

 membranes, afford very great facilities for respiratory gas 

 exchange and local blood purification, with consequent 

 vital effects on the superimposed cerebral structures. 



Each inspiration and expiration balances the other, and 

 constitutes an act of respiration, but how different, in 

 the chemical and physical character of their respective 

 gases and vapours, they are ! Inspiration passing in, it 

 should be, the purest of air to the exposed blood, while 

 expiration receives, for elimination, the residual gaseous 

 products of chemico-physiological activity and tissue 

 waste. 



The first respiration and the last mark the beginning 

 and end of independent life, and form the terminal 

 extremities of that longer or shorter " breath of life" 

 which constitutes the "span" of human existence. As 

 the vehicular requirements of the process of nutrition are 

 met by the principle of aqueous circulation of material 

 plasma, in mass and in molecule, so are its specific final 

 metabolic phenomena met by the physiologico-chemical 

 activities of atmospheric air, and the structural integrity 

 and life of the tissues maintained in normal physiological 

 condition, material and dynamic, by its oxydising and 

 de-oxydising influences in the processes of tissue integra- 

 tion and disintegration. 



