440 DISEASES OF THE CIRCULATORY SYSTEM. 



where the heart is covered up by a portion of the lungs, a deep per- 

 cussion reveals, however, a localized duluess between the fourth 

 and sixth ribs. In other animals, the cardiac dulness, when it i& 

 perceptible, gives but vague information, on account of the very 

 reduced dimensions of the heart. Sub-dulness may be due to the 

 augmentation of the volume of the lung (emphysema), also to 

 dextro-cardia, pneumothorax, or pueumo-pericardium; the increased 

 dulness is produced by cardiac hypertrophy, dilatation of the heart, 

 exudative pericarditis, hydro-pericarditis, atrophy or retraction of 

 the left pulmonary lobe (tuberculosis, glanders) ; dextro-cardia 

 may result from a pleuritic exudate, hydrothorax, and pulmonary 

 hepatization ; anteversion of the heart is the consequence of tym- 

 panites ; backward displacement is caused by the adhesions of the 

 pericardium to the diaphragm or to the lung, etc. 



II. The weight of the heart, in animals of the same species, varies 

 according to the size, the race, the constitution, age, service, etc. 

 Slight or average increase or lessening of this weight are difficult 

 to recognize. It is proper to take as a base the relation existing 

 between the weight of the body and that of the heart. In the 

 horse this relation is 1 per cent. (0.7 to 1.1 per cent., according to 

 Franck) ; the absolute weight of the heart varies between 2 and 7 

 kilos; as a general rule, when this organ weighs more than 4 J 

 kilos (except when the horse is of extraordinary size or of a fine 

 breed), it must be considered as hypertrophied. The relation be- 

 tween the thickness of the right and left cardiac walls is as 1 : 2.5. 

 (In the horse, this thickness is 2 centimetres on the right and 3J 

 centimetres on the left.) 



In the ox and sheep, the weight of the heart is to that of the 

 body as 1 : 220 (Colin); this proportion is nearly the same in the 

 pig ; in the dog it is as 1 : 90 (Colin, Negrini), and according to 

 Raabe, of 1.4 per cent, on an average. 



III. In all domestic animals the cardiac or precordial bruit is 

 normally perceptible at the surface of the fifth rib. In healthy 

 carnivorous animals, it is felt on both sides of the chest, because the 

 heart is situated nearer the median line and the diaphragm. The 

 normal cardiac blow is very feeble in the horse, where it is only 

 perceptible on the left ; in horses of strongly developed muscles it 

 is imperceptible. The number of pulsations is on an average 28 

 per minute in the stallion, from 33 to 39 in the gelding, from 34 

 to 40 in the mare, from 40 to 60 in the ox, from 70 to 80 in the 



