OP RESPIRATION. 149 



however, considerations of a still weightier character, which must compel 

 us to adopt it. The affinity between the blood and the parts with which 

 it is brought in contact is a chemical fact beyond contradiction. The 

 pressures and motions I have been speaking of follow as the inevitable 

 consequences of that affinity. We can not, therefore, gainsay their ex- 

 istence in the living mechanism, and the only doubt we can entertain is 

 as to whether they are of competent power to produce all the effects be- 

 fore us. But after what has been already said respecting the energy of 

 endosmotic movements displayed against pressures of many atmospheres, 

 we may abandon those doubts ; and since we have here a force of uni- 

 versality enough, and intensity enough, and in every instance acting in 

 the right direction, it would be unphilosophical to look farther, since such 

 a force must, under these conditions, exist in the physical necessity of 

 the case. 



CHAPTER IX. 



OF RESPIRATION. 



Respiration introduces and removes aerial Substances. Coalescence of Respiratory and Urinary 

 Organs in Fishes. Physical and chemical Conditions of Respiration. Interstitial Movements 

 of Solids, Liquids, and Gases. Condition of Equilibrium in the Diffusion of Gases. Con- 

 densing Action of Membranes. Forms of Respiratory Mechanism. The Lungs of Man. 

 Three Stages in the Introduction of Air: Atmospheric Pressure, Diffusion of Gases, and 

 Condensation by Membranes. Exchange of Carbonic Add for Oxygen. Divisions of the Con- 

 tents of the Lungs. Variations in the expired Air. Removal of Water. Effect ofirrespira- 

 ble Gases. Experiments ofRegnault and Reiset. Nervous Influence concerned in Respiration. 

 Results of Respiration. 



SINCE it is essentially necessary to the life of all animals that the 

 blood should pass to every part of the system, provision must objects of 

 be made for securing aeration. The breathing apparatus is the res P irati on. 

 skin, or some extension, reflection, or modification of it. 



Besides the great duty of originating the circulation, respiration is con- 

 nected with others of equal importance. The functional activity of the 

 nervous and muscular tissues is dependent on their- oxidation, and this 

 implies the introduction of air. In each tribe, moreover, it is necessary 

 to keep the temperature up to a specific point. This also is accomplished 

 by oxidation, either of the disintegrating material which is passing to 

 w^aste, or of combustible substances, such as sugar or fat. 



All organic material, at its death, eventually gives origin, .p. 

 under the action of the air, to two products with which the of tissue meta- 

 function of respiration is mainly concerned. These products mor P hosis - 

 are carbonic acid and water. With the exception of gelatin, the other 



