300 CIRCULATORY APPARATUS. 



hyperplastic induration, with which we became acquainted in 

 chronic endocarditis. The general effect of the changes in 

 question is a cicatricial stricture of the orifice. White, glisten- 

 ing bands of connective tissue are put on the stretch whenever 

 we try to open out the cut edges of the coims arteriosus. The 

 valves usually appear puckered and thrown into folds, as though 

 their base of attachment had been narrowed. Moreover, the 

 development of all the affected parts appears to have been 

 retarded; they are small and dwarfed. The canal is usually 

 constricted to a degree hardly short of absolute closure ; the 

 effects of this constriction are highly complex, owing to the fact 

 that it occurs at a period in the development of the heart, when 

 its separation into a right and a left half is not yet complete. 

 Let us suppose in the first place that the right ventricle cannot 

 discharge its contents through the pulmonary arteries ; and let 

 us inquire through what channels it does discharge them? 

 Through the aorta. The septum ventriculorum is still imper- 

 fect ; growing upwards from the apex, it has not yet become 

 attached to the base. It is jDushed over towards the left ven- 

 tricle, so that the dilated orifice of the aorta comes to be placed 

 over the right as well as the left ventricle, comes to spring from 

 both ventricles at once. If we consider further, that by oblitera- 

 tion of the pulmonary trunk, the chief mode of access to the 

 pulmonary circulation is cut off, we are led to inquire how the 

 lungs receive their supply of blood? In the first place, they 

 receive less blood than they ought ; the blood accumulates in the 

 venous portion of the systemic circulation ; this is the chief cause 

 of the incessant dyspnoea from which persons afflicted with this 

 malformation suffer. Moreover the blood which the lungs do 

 not receive through the contracted pulmonary artery, reaches 

 them from the aorta, partly through the ductus arteriosus Botalliy 

 which remains pervious, partly through the bronchial arteries, 

 whose anastomoses with the pulmonary circulation undergo 

 marked dilatation in these cases. Meanwhile it is quite clear that 

 all these arrangements, even when they attain their maximum 

 degree of efiiciency, can only afford a sorry compensation for 

 the disturbances produced. For just as in the single-chambered 

 heart of fishes, the arterial and venous blood are mingled in the 

 aorta. The lungs receive blood which is only half venous, and 

 are in consequence less capable of removing the carbonic acid of 



