DISEASES OF THE OX AND SHEEP. 177 



lymph. When a portion is examined with the microscope, cells, 

 like the colourless corpuscles of the blood, and like pus cells, 

 are found embedded in it. No doubt they are of the same nature 

 as these cells. The fluid in the chest and the false membranes 

 may be considerably less in the pleural cavity on one side of 

 the chest than in that of the other. The lungs may be also 

 united by bands of fibrin (which are easily broken) to the heart- 

 bag (pericardium), and also to the midriflp (diaphragm). The 

 tissue connecting the cardiac fat is thickened. The lining 

 membranes of the lungs, as well as those of the chest-walls, and 

 also the bronchial tubes and blood-vessels, are all affected. 

 There is, in fact, an extensive exudation of a yellowish fluid, 

 called serum or coagulable lymph, in the lungs and the struc- 

 tures closely connected with it. This coagulates to a greater 

 or less extent, and thus portions of the lung or lungs become 

 mechanically obstructed. 



It is said that the first change is that the blood-vessels of one 

 or both lungs dilate. If the animal is killed soon after being 

 attacked by the disease, a more distinct scarlet hue may be noted 

 in the aff'ected lung or lungs. These organs, being full of blood 

 and of the products of the abnormal processes going on, are 

 consequently heavier, and sink further in water than healthy 

 lungs do. As the disease proceeds, they become heavier and 

 heavier. A healthy lung floats in water, has a bright salmon 

 colour, is smooth, elastic, and yielding, and weighs about 6^ lb. 



The detached lungs of an animal that has died of pleuro- 

 pneumonia are enormously heavy. Indeed, one diseased lung 

 alone may weigh as much as 301b. The two have been known 

 to weigh from 201b. to as much as 751b., or even 1 cwt. The 

 pleural linings are rough and thick, and the lung substance is 

 hard and inelastic. Being consolidated in a greater or less degree, 

 they resist pressure and do not crepitate when incised, owing to 

 the air-cells being blocked up. It is readily seen that such 

 lungs cannot fill themselves with air by expanding, and empty 

 themselves by contracting. In other words they cannot fulfil 

 the function of breathing. 



If the lung is cut with a knife, the exposed surfaces present 

 an appearance most characteristic of this disease. It has been 

 termed a "marbled" appearance. This same aspect is seen in 

 the cut surface of the lung of a horse which has died of pleuro- 



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