RESPIRATION. 67 



is the real agent in the respiratory process, and that the corpuscles 

 are the carriers of oxygen into the system, and of carbonic acid out 

 of it. He supposes the iron to exist in the form of protoxide in venous 

 blood, united with carbonic acid, forming a carbonate of the pro- 

 toxide of iron ; in the lungs, the carbonic acid is given off, leaving 

 the protoxide, which by union with half an equivalent of oxygen, is 

 converted into the peroxide, at the same time that the colour is 

 changed to arterial. In the systemic capillaries the reverse takes 

 place, — the oxygen being imparted to the tissues, and replaced by 

 the carbonic acid, which is given up by them to be conveyed out of 

 the system. 



Mulder, Scherer, and others, account for the change of colour, by 

 a change o^ form in the red corpuscles, which are supposed to be 

 bi-concave, and reflecting bodies in arterial blood, and bi-convex, 

 and refracting bodies in venous blood. Mulder shows that the 

 colour is not dependent on the presence of iron, since it is retained 

 when all the iron has been entirely removed. 



The presence of a certain amount of saline matters appears, from 

 the experiment of Dr. Stevens, to be essential for the due influence 

 of oxygen upon the colour of the blood ; since, if they be deficient, 

 the contact of oxygen will not produce its usual effect. 



The blood parts with a considerable amount of water in the lungs, 

 amounting to 16 or 20 ounces in 24 hours. It also absorbs volatile 

 matters from the air. The water contains some animal matters, and 

 has its source, according to Dr. Prout, in the chyle which has just 

 been poured into the blood ; probably also it escapes by evaporation 

 through the thin animal membrane. 



Asphijxia, — If from any cause the supply of oxygen be cut off*, 

 a condition ensues to which the name of asphyxia has been given ; 

 the essential character of which, is the cessation of -muscular move- 

 ment, and shortly afterwards of the circulation, with an accumula- 

 tion of blood in the venous system. The time necessary for the 

 production of this state is inversely proportionate to the development 

 of the respiratory function ; thus, warm-blooded animals are much 

 sooner asphyxiated than reptiles. In the former, deprivation of air 

 for two minutes is sufficient to produce insensibility and loss of mus- 

 cular power. The circulation generally fails within ten minutes. 



The first effect of non-arterialization of the blood in the lungs, is 

 the retardation of the fluid in their capillaries, an accumulation in 

 the venous system, and a deficient supply to the arterial. The ope- 

 ration of these two causes arrests the action of the heart, although 

 the eff*ect on the two sides is different ; the right side ceases to act 

 from over-distention ; the left, from deficiency of stimulus to excite 

 the movement. If the stoppage have not been too long, the heart's 

 action may be renewed by artificial respiration ; for the replacement 

 of oxygen in the air cells, restores the pulmonary circulation, 



