▼OL. LXXXVII1.] PHILOSOPHICAL TRANSACTIONS. 289 



there seems to arise a necessity for similar openings on the left side; but these, in 

 their natural state, though capable of emitting blood, and of relieving the plethora 

 of the coronary vessels, are not of sufficient size to give passage to common waxen 

 injections. Yet, when there is a distended state of the right cavities of the heart, 

 which is almost certainly occasioned by a diseased state of the lungs, these fora- 

 mina leading into the left cavities then become enlarged, in the manner that has 

 been already described; and thus the plethoric state of the nutrient vessels of the 

 heart, and the consequent disease of that important organ, are prevented. The 

 preceding remarks will, I think, sufficiently explain the cause of the variety in the 

 size and situation of these foramina, which also appear to belong both to the arteries 

 and veins; because the injection which was employed was too coarse to pass from 

 one set of vessels to the other, and yet the different coloured injections passed into 

 the cavities of the heart unmixed. 



There is vet another mode by which diseases of the heart, that would otherwise 

 so inevitably succeed to obstruction in the pulmonary vessels, are avoided; and 

 which I next beg leave to explain. Having formerly been much surprized to find 

 the heart so little affected, when the lungs were greatly diseased, and observing, in 

 one or two instances, that the foramen ovale was open, I was led to pay more par- 

 ticular attention to the state of that part; and I have found this to be almost a con- 

 stant occurrence in those subjects where pulmonary consumption had for some time 

 existed previous to the person's decease. I took notice of this circumstance 13 

 times in the course of one year; and in several instances the aperture was suffi- 

 ciently large to admit of a finger being passed through it. Now, as the septum 

 auricularum is almost constantly perfect in subjects whose lungs are healthy, I can- 

 not but conclude, that the renewal of the foramen ovale is the effect of disease; 

 nor will the opinion appear on reflection improbable; for the opening becomes 

 closed by the membranous fold growing from one edge of it, till it overlaps the 

 other, and their smooth surfaces being kept in close contact, by the pressure of the 

 blood in the left auricle, they gradually grow together. But, should there be a 

 deficiency of blood in the left auricle, and a redundance in the right, the pressure 

 of the latter on this membranous partition, will so stretch and irritate the uniting 

 medium, as to occasion its removal; and thus a renewal of the communication be- 

 tween the auricles will again take place. 



From these observations it is natural to suppose, that in those men, or animals, 

 who are accustomed to remain long under water, this opening will either be main- 

 tained or renewed; yet on this circumstance alone the continuance of their life does 

 not depend; for we now have sufficient proof, that if the blood is not oxygenated 

 in the lungs, it is unfit to support the animal powers. There is an experiment 

 related by Buffon, the truth of which I believe has not been publicly controverted, 

 and which tends greatly to misrepresent this subject. He says, that he caused a 

 bitch to bring forth her puppies under warm water; that he suddenly removed them 

 into a pail of warm milk; that he kept them immersed in the milk for more than 



vol. xviii . P p 



