S36 Sir E. Home's Additions to an Account 



water of much depth, the ventricle is so weak, that the supply 

 of blood to the gills is regulated by the contraction and re- 

 laxation of a muscular valve. 



As water, according to the degree of pressure upon it, is 

 capable of containing a greater quantity of atmospherical air, 

 than under ordinary circumstances, such a supersaturated state 

 of the water might compensate, with respect to the respiration 

 of fishes, for the difficulties, which occur at great depths, of 

 forcing the blood through the vessels of the gills : I enquired 

 what evidence could be produced, of the water at great depths 

 containing a more than ordinary quantity of air ; my philoso- 

 phical friends, to whom I proposed this question, said, that it 

 was a point that had not been considered. I therefore resolved 

 to put it to the test of experiment, and as I knew there was a 

 well at Mr. CouTTs's in the Strand, which more than twenty- 

 five years ago had been sunk four hundred feet below the 

 surface of the water in the Thames, I requested permission to 

 make the experiment in that well. A cylindrical vessel, with 

 a valve above and below, was let down to the depth of one 

 hundred and eighty-six feet, which is now the depth of the 

 well ; it came up full of clear water, which Mr. W. Brande 

 ascertained to contain no greater proportion of atmospherical 

 air, than is met with in common river water. It therefore ap- 

 pears that the supply of air to fishes is nearly the same at 

 whatever depth they are from the surface. 



Besides the guards which have been mentioned, to prevent 

 the circulation through the gills from being improperly carried 

 on, in particular tribes of fishes, the ventricle itself is so 

 formed, and is so situated with respect to the auricle, that the 

 blood received is first impelled in a direction nearly at right 



