72 DISEASES OF THE PERICARDIUM 



and placing the right ear directly over it. A phonendoscope 

 may be used which materially assists in differentiating the 

 heart sounds, the instrument greatly intensifying them. 

 Normally, there are two heart tones. One of these occurs 

 at the moment of contraction of the heart (systolic), and 

 the other at the dilatation of the organ (diastolic). In most 

 small animals the rapid pulse makes it difficult to distin- 

 guish between these sounds. It is therefore best to com- 

 pare the pulse with the heart beat. The interval between 

 the systolic and diastolic sounds is shorter than the one 

 between the diastolic and systolic. In very fat animals it 

 is difficult to distinguish the heart tones with any degree of 

 accuracy. In rabbits and cats the heart tones are often so 

 rapid, the sounds following each other in such rapid succes- 

 sion, that they are indistinguishable. This condition occurs 

 in all animals after excitement or exercise. In very young 

 animals it is normal. In birds the heart sounds are almost 

 impossible to recognize. 



Both of these heart sounds are increased in hypertrophy 

 of the heart, anemias, and thickening of the lung tissue 

 around the heart. 



The second or diastolic sound is increased in distention 

 of the arteries, often the result of a congestion of the pulmo- 

 nary circulation combined with hypertrophy of the heart. 



A decrease in the volume of the heart sounds is observed 

 in heart weakness, such as degeneration of the heart muscle, 

 in hydropericardium, and in emphysema of the lung. In 

 many of these cases the heart sounds are imperceptible. In 

 small animals the various heart bruits (abnormal sounds) 

 are often difficult to recognize. 



It will require careful and persistent effort on the part of 

 the student to familiarize himself with even the more common 

 bruits which are the following: (1) Endocardial, and (2) 

 pericardial. 



1. Endocardial Bruits are divided into: (a) Organic 

 endocardial bruits which are caused either by a narrowing 

 (stenosis) of the valves of the heart, or changes in the valves 

 which interfere with their proper closing (insufficiency). 

 (b) Inorganic endocardial bruits occurring without any 



