THEORY OF RESPIRATION. 383 



we prescribed Lichen Carragheen, or Ol.jccoris Asell'i. Instead of 

 tormenting an emphysematous patient, suffering from congestion 

 and hsemorrhoidal tendencies, with aperients and saline mineral 

 Avaters, we might relieve him far more effectually by recommending 

 him to practice artificial augmentation or expansion of the chest 

 in respiration (filling the lungs several times in the course of an 

 hour), or to take exercise suited to produce this result, while we 

 should forbid the use of spirituous drinks, and not prescribe 

 tinctures, which might hinder the necessary excretion of carbonic 

 acid. We abstain, however, from offering any further illustrations 

 of these assertions, since the reflecting physician will not blindly 

 follow any guide ; while the mere empiricist can never learn 

 thoroughly to heal any disease, whatever may be his knowledge of 

 physiology and pathological chemistry. 



We endeavoured, at the beginning of this section, to give a 

 general representation of the interchange of gases which occurs 

 within the lungs, tracing the movements of the atmospheric air 

 into the pulmonary vesicles, where an opposite current of gases is 

 developed from the fluid blood-. What we then regarded almost 

 a priori as a physical necessity in this occurrence of two opposite 

 currents of air, has been proved, from Vierordt's experiments, to 

 be an actual fact. Mechanical forces, considered in the strictest 

 sense of the word, were insufficient to carry the oxygen into the 

 pulmonary vesicles and the carbonic acid into the trachea, as has 

 been most conclusively proved by the suggestive experiments of 

 Hutchinson* and others. There is one portion of their course 

 through which the oxygen and carbonic acid must be propelled by 

 the aid of diffusion; and this, as Vierordt has shown by the 

 numerous modifications of his experiments on respiration, is 

 controlled by the same laws which Grahamf has expounded in so 

 masterly a manner. We may, therefore, hope that we have 

 arrived at the recognition and physical explanation of the inter- 

 change of gases effected within the air-passages. We have thus, 

 as it were, arrived at the boundaries of the blood in our theoretical 

 consideration, and it now only remains for us to explain the 

 physical or chemical laws by which the gases dissolved in the 

 blood are liberated, and those of the atmosphere are condensed in 

 the blood. Having acquainted ourselves with the constitution of 

 the air at the place of its exchange that is to say, in the pul- 



* Medico-chirurgical Transactions, Vol. 29, pp. 137-152 ; and Cyclopaedia of 

 Anatomy and Physiology, Vol. 4, pp. 1016-1087. 



t Trans, of Boy. Soc. of Edin. Vol. 12, p. 222. 



