FOUL AIR AND DISEASE OF THE HEART. 189 



carbonic acid in the air respired upon the contractility of the muscular 

 fibres of the heart. 



I take for my example the newly-hatched trout. During the win- 

 ters of 1869-'70 and 1870-'71, I hatched some thousands of this fish, 

 many of which I daily submitted to microscopical examination. The 

 result of my investigations, in reference to the action of the "heart and 

 to the influence upon it of a decreasing quantity of oxygen and an in- 

 creasing quantity of carbonic acid in the water in which the fish was 

 confined, shows 



That, on placing the fish in a glass trough containing a quantity of 

 water, the heart is seen, under the microscope, to be affected in the 

 following manner: 



In the first few moments of examination the venous blood, collected 

 by the veins from the head, back, and yelk-bag (the first two of which 

 unite to form a bulbous vessel into which the third opens), is seen to 

 be projected with considerable force and rapidity into the upper (au- 

 ricle) of the two cavities of which the heart is composed, and thence 

 as instantaneously into the lower (ventricle) cavity, which contracts 

 with equal rapidity, and forces the blood into the branchial artery, 

 which conveys it to the gills. The projection of the blood into the 

 auricle, its passage into the ventricle, and its expulsion therefrom, are 

 but the work of an instant. As the blood enters the auricle, both it 

 and the ventricle seem to anticipate the charge of blood ; but espe- 

 cially is this the case with the ventricle. Before the blood well touches 

 the valve which guards the entrance from auricle to ventricle, the lat- 

 ter is observed to shorten its longitudinal diameter, to visibly meet, 

 as it were, the coming charge of blood from the auricle, and to force 

 it instantly into the branchial artery. There is no delay whatever of 

 the blood in the auricle or ventricle. It is shot in a straight line from 

 the vena cava through the auricle and the auriculo- ventricular valve, 

 caught by the contracting ventricle, and deflected and forced, without 

 a moment's delay, into the branchial artery. 



From these observations it was evident that the contraction of the 

 heart was not excited by the distention of its cavities, but that it was 

 induced by the mere impingement of the blood upon its lining mem- 

 brane. In contracting, the ventricle was seen to roll about one-third 

 upon its axis, by which a portion of that part of it which was pre- 

 viously out of sight was brought into view. As soon as it had deliv- 

 ered its blood into the branchial artery, it relaxed, and increased again 

 its longitudinal diameter, recoiling from systole with an energy and a 

 rapidity equal to those of its contraction. 



In three or four minutes the heart is observed to contract both less 

 quickly and less energetically. A very short time after this the blood 

 can be seen gently pouring into the auricle, and thence into the ven- 

 tricle, which latter now allows itself to be about one-fourth filled be- 

 fore it contracts. It now expels its blood, and again dilates ; but its 



