40 ACTION IN ASPHYXIA, ETC. 



him objects for which it has been adjusted, and those in an unsatisfactory manner; but 

 if he moves to one side or to the other, or endeavours to see objects which are not di- 

 rectly in his way, his view is intercepted, or, perhaps, unless he makes a new adjust- 

 ment, the light is shut out altogether. 



131. Let us, therefore, see how these chemical principles will apply when the sys- 

 tem under consideration is no longer under normal conditions, but has passed into a 

 state of disturbance or of disease. It is well known to physicians, from the phenomena 

 of asphyxia, that whenever the admission of oxygen into the air-cells of the lungs is 

 prevented, the circulation through them simultaneously stops ; but it may be renewed 

 again on the readmission of that gas, provided it is within a short space of time, and 

 recovery may and often does take place under these circumstances. What, now, is the 

 cause of that asphyxiated condition ? why does the blood cease to flow ? The chem- 

 ical theory of the circulation of the blood through the lungs, which I have just given, 

 points to the oxydation of that blood as the very cause of its movement (116). It is 

 the pressure of the deoxydized upon the oxydized blood that drives the latter along the 

 pulmonary veins to the heart. But should anything intervene to prevent that oxyda- 

 tion taking place, no pressure can arise, and, therefore, no movement can ensue ; the 

 conditions for asphyxia are all present ; conditions which, however, are removed so 

 soon as oxydation can be reaccomplished ; then movement once more takes place, and 

 a natural state is restored. If any evidence were required to show how little influence 

 the heart possesses in controlling the pulmonary circulation, and how much depends on 

 the oxydation of the blood, it may be derived from the phenomena of asphyxia. 



132. As another illustration, we may here bring forward and explain the fact, well 

 known to physiologists, that if the trachea be obstructed so that oxygen is restrained 

 from passing into the lungs, and asphyxia is being induced, blood taken from any of 

 the systemic arteries exhibits a venous aspect. What, now, does the chemical theory 

 say should take place in the general circulation? We are to remember (114) that the 

 very cause of that circulation arises from the pressure of the oxydized arterial blood 

 upon the deoxydized venous blood. Under the conditions supposed, we have inter- 

 fered with the constitution of the arterial blood, and given it a venous character; the 

 conditions for pressure are, therefore, not accomplished, and no pressure takes place, 

 and no flow from the arterial to the venous capillaries. Under these circumstances, the 

 impulsive action of the left ventricle must be spent in an increased pressure on the 

 walls of all its communicating arteries, and a simultaneous relief of pressure takes effect 

 on the walls of all the veins. As, in a steam-engine, any steady variation of motion is 

 finally impressed upon the governor, which adjusts itself consentaneously ; so, in this 

 case, the heart, which acts as a governor, accommodates itself to the changes going on. 

 The left ventricle presently ceases in its violent effort to force the blood, and the pres- 

 sure on the arterial walls abates. But, if the trachea is now relieved, oxydation of the 

 blood goes on, pressure again takes place in the systemic capillaries, and the proper 

 action is restored. 



133. These different facts, which might have been predicted from the theory that 

 the deoxydation of arterial lilobd is the cause of the systemic circulation, have every 



