ANATOMICAL CHARACTERS. 533 



may be effused. In the earlier stages there would appear to 

 exist in the pleuritic eftusion a greater proportion of plastic 

 and coagulable fibrinogenous material than at other periods, 

 whilst it is at this time^ also that we observe the colour of the 

 liquid is darkest, being mingled with blood or blood-colouring 

 from capillary haemorrhage. 



Although there may be a gradual tendency with age for 

 the fluid to become clearer, partly by the subsidence of the 

 heavier particles and absorption of others, while the latter 

 exudate is more purely serous, I am inclined to attribute this 

 difference in character and colour in no small degree to 

 original difference in the effusion itself, which again is closely 

 related to the type of the diseased action. 



In all cases of pleurisy, where the effusion into the pleural 

 sac is considerable, we find that the pulmonary tissue has 

 undergone considerable change. It is of less bulk, not so clear 

 in colour, collapsed, and on manipulation has lost, to a greater 

 or less extent, its resilience ; still it is not like the solidification 

 of pneumonia ; it may, as a rule, be inflated, the pulmonary 

 vesicles not being destroyed. When incised it is dry and light- 

 coloured, and feels tough, both air-cells and intercellular 

 tissue being free from infiltration or deposit. This condition 

 of collapse is chiefly the result of pressure of the pleuritic 

 fluid, probably also influenced by the inflammatory action pro- 

 pagated to the integral pulmonic textures. 



Pleurisy may attack the membrane linmg both cavities of 

 the chest, or it may be confined to one, oftener the right. 

 When there is much serous fluid exuded into the pleural sac 

 of one side, we may from the normal perforated condition 

 of the pleural septum, the mediastinum, expect to find it 

 at the same time occupying the other also. This is, how- 

 ever, not invariable, seeing that from the results of in- 

 flammatory action, this condition of perforation may be 

 obliterated, and the fluid confined to the side where exuded ; 

 or, in some instances, the liquid product may be enclosed in 

 loculi or spaces formed by the more consistent exudate. 



Symptoms. — In the horse, pleurisy in its acute form is readily 

 known and well marked by several leading features. Generally 

 ushered in by some slight chilliness or more perfectly marked 

 rigor, followed by fever, succeeded by quick and careful breath- 



