VOL. LXXXVIII.] PHILOSOPHICAL TRANSACTIONS. 335 



the combination of a certain quantity of oxygen gas with it. In passing from the 

 arteries to the veins, in every part of the body except the lungs, it loses the florid 

 hue, and becomes darker : the florid blood is that which is employed for the pur- 

 poses of supporting life. In the natural circulation, it is well known that the whole 

 of the blood conveyed to, and circulating in, the pulmonary artery, is of a dark 

 colour; and the whole of it, when returned by the pulmonary veins, is florid. 



It is obvious, in the case which has been described, that there always must have been 

 florid and dark-coloured blood, mixing and circulating in the arteries. It would seem 

 also, on the first reflexion, that the quantity of dark-coloured blood would be the 

 greatest, in the same proportion as the capacity of the aorta was larger than that 

 of the pulmonary artery. It is therefore necessary to recollect, that a considerable 

 proportion of the blood carried to the lungs was already florid or oxygenated; and 

 also, that the lungs in this infant were larger in proportion, than in children of 

 the same age: a smaller quantity of blood therefore was to be oxygenated, and 

 a larger surface than usual was appropriated for this purpose. It appears also, from 

 experiments, such as making a person breathe air in which there is a greater pro- 

 portion of oxygen gas than in our atmosphere, that the blood can combine with 

 more of it than it does in natural respiration : it therefore is not an improbable 

 supposition, that a larger quantity was combined here. A small drawback must be 

 allowed, for the quantity of oxygenated blood used in the support and secretions 

 of the lungs, and which is usually conveyed to them by the bronchial artery; but 

 this quantity is too small to require more than this slight observation of it. The 

 blood also which passed to the lungs, must have been again conveyed to the heart 

 sooner, from the shortness of its circuit; and must have entered the heart with 

 a quicker or stronger current, than that blood which passed to, and was returned 

 from, the more remote parts of the body; as, in this child, the pulmonary artery 

 and aorta were filled by the contraction of the same ventricle. In the hearts of 

 other children, some time after birth, the muscular fibres of the right side are 

 much fewer in number than in the left. 



If these circumstances are admitted as fact, viz. that the blood circulating through 

 the lungs of this child was combined with a larger proportion of oxygen gas, and 

 was returned in a quicker and stronger current into the auricle than that returned 

 by the venae cavae, it seems reasonable to infer, that this blood, mixing and blend- 

 ing with the dark or unoxygenated blood, would render the whole nearly as much 

 oxygenated as it usually is found in the left side of the heart, and in the aorta; 

 therefore, that the blood circulating in the arteries of this child would be fully equal 

 to the support of life. Previous to birth, this peculiarity of structure could not 

 affect its health or growth, as the placenta then answers the purpose which the 

 lungs do afterwards; and the single ventricle seemed as equal, from its size, to 

 propel the blood on to the placenta, as both ventricles in the natural state are, by 

 means of their communication through the ductus arteriosus.* 



* It is here not unworthy of remark, that the circulation in this child, after its birth, was in several 



