324 Veterinary Medicine. 



ticipate in turn in the internal pressure and dilatation. The right 

 ventricle is more often affected than the left, because of the 

 greater frequenc}- of obstruction in the circulation through the 

 lungs than in that through the general system, and because of the 

 thinness of its walls which more readily give way under internal 

 pressure. Dilatation may result from disease of the great arteries, 

 from diminution of their calibre by the pressure of tumours, or by 

 narrowing of their openings at the heart, whether as the result of 

 diseased valves or other morbid condition. As affecting the 

 auricles primarily its usual cause is narrowing of the auriculo- 

 ventricular opening from some abnormal deposit. The extreme 

 thinness of the walls of the auricles allows these to give way un- 

 der internal pressure even much more readily than the right 

 ventricle. 



The causes it will be seen are similar to those inducing hyper- 

 trophy, and hence the frequent coexistence of the two. Pure 

 dilatation occurs especially when internal pressure takes place 

 suddenly and to excess, and while the nutritive functions are to a 

 great extent in abeyance. Such conditions are found in acute 

 inflammations of the respiratory organs, or of the inner or outer 

 membranes of the heart, and the rapid deposit in the lungs of 

 tubercles or other abnormal material. 



Dilatation of the right side of the heart is a common complaint 

 in overfed cattle, and is apparently due to the diminished power 

 of resistance in the walls of the heart, the muscular substance of 

 which is partly replaced by fatty granules, and to the obstruction 

 offered to the circulation by the extraordinary accumulation of fat 

 around the base of the heart and the commencement of the large 

 blood vessels. Though a diseased condition this rarely shortens 

 life or interferes with the uses to which cattle are put. 



The heart walls are similarly weakened and yield more readily 

 to the internal blood pressure in endocarditis, myocarditis, peri- 

 carditis, high fever, infectious diseases, poisonings, anaemia, and 

 debilitating diseases generally. Debility and incapacity to resist 

 the blood pressure is the essential prerequisite to dilatation. 



The sympto7ns which have been already enumerated in the 

 table given under the head of hypertrophy are mainly these : Loss 

 of appetite, spirit and endurance ; faintness and difficulty of 

 breathing on the slightest exertion ; habitual coldness with a 



