182 CONTENTS OF THE CHEST. 



the pulmonary system ; but, united in the manner in which they a:e, th, i juncti >n 

 contributes to their mutual strength, and both circulations are carried on at the same 

 time 



Th" first is the arterial circulation. No function can be discha-ged life cannot 

 exist, without the presence of arterial blood. The left ventricle that contains it con- 

 tracts, and by the power of that contraction, aided by other means, which the limits 

 of our work will not permit us to describe, the blood is driven through the whole 

 arterial circulation the capillary vessels and the veins and returns again to the 

 heart, but to the right ventricle. The other division of this viscus is likewise 

 employed in circulating the blood thus conveyed to it, but is not the same fluid which 

 was contained in the left ventricle. It has gradually lost its vital power. As it has 

 passed along, it has changed from red to black, and from a vital to a poisonous fluid. 

 Ere it can again convey the principle of nutrition, or give to each organ that impulse 

 or stimulus which enables it to discharge its function, it must be materially changed. 



When the right ventricle contracts, and the blood is driven into the lungs, it passes 

 over the gossamer membrane of which the lobules of the lungs have been described 

 as consisting ; the lobules being filled with the air which has descended through the 

 bronchial tubes in the act of inspiration. This delicate membrane permits some of 

 the principles of the air to permeate it. The oxygen of the atmosphere attracts and 

 combines with a portion of the superabundant carbon of this blood, and the expired 

 air is poisoned with carbonic acid gas. Some of the constituents of the blood attract 

 a portion of the oxygen of the air, and obtain their distinguishing character and pro- 

 perties as arterial blood, and being thus revivified, it passes on over the membrane of 

 the lobes, unites into small and then larger vessels, and at length pours its full stream 

 of arterial blood into the left auricle, thence to ascend into the ventricle, and to be dif- 

 fused over the frame. 



DISEASES OF THE HEART. 



It may be readily supposed that an organ so complicated is subject to disease. It 

 is so to a fearful extent; and it sympathises with the maladies of every other part. 

 Until lately, however, this subject has been shamefully neglected, and the writers on 

 the veterinary art have seemed to be unaware of the importance of the organ, and the 

 maladies to which it is exposed. The owner of the horse and the veterinary profes/- 

 sion generally, are deeply indebted to Messrs. Percivall and Pritchard* for much 

 valuable information on this subject. The writer of this work acknowledges his 

 obligation to both of these gentlemen. To Dr. Hope also, and particularly to Laennec, 

 we owe much. Mr. Percivall well says, "This class of diseases may be regarded as 

 the least advanced of any in veterinary medicine a circumstance not to be ascribed 

 so much to their comparative rarity, as to their existing undiscovered, or rather 

 being confounded during life with other disorders, and particularly with pulmonary 

 affections." 



The best place to examine the beating of the heart is immediately behind the 

 elbow, on the left side. The hand applied flat against the ribs will give the number 

 of pulsations. The ear thus applied will enable the practitioner better to ascertain 

 the character of the pulsation. The stethoscope affords an uncertain guide, for it can 

 not be flatly and evenly applied. 



PERICARDITIS. The bag, or outer investing membrane of the heart, is liable 

 inflammation, in which the effused fluid becomes organized, and deposited in layers, 

 increasing the thickness of the pericardium, and the difficulty of the expansion and 

 contraction of the heart. The only symptoms on which dependence can be placed, 

 are a quickened and irregular respiration ; a bounding action of the heart in an early 

 stage of the disease; but that, as the fluid increases and becomes concrete, assuming 

 a feeble and fluttering character. 



HYDROPS PER^CARDII is the term used to designate the presence of the fluid secreted 

 in consequence of this inflammation, and varying from a pint to a gallon or more. 

 In addition to the symptoms already described, there is an expression of alarm and 

 anxiety in the countenance of the animal which no other malady produces. The 

 horse generally sinks from other disease, or from constitutional irritation, befcre ths 



* See Pritchard's papers in the Veterinarian, vol. vi., and Percivall's Hippopatholcgy, oJ 

 &, Part I 



