Anatuuiical Changes. 163 



of pleuritis solely produced by cold. The present authors look 

 upon cold as merely an exciting, predisposing cause which 

 makes possible the invasion of the pleura by bacteria living 

 in the animal body or gaining access accidentally or causing 

 a general infection. It is self-evident that the predisposing 

 influence of a cold may be so important that without this factor 

 bacteria would not be able to manifest their pathogenic effect. 

 Cadeac is of the same opinion, and Dieckerhoff believes that 

 infectious bacteria play a role in connection with taking cold. 



The fact deserves nieution that Laborde and Trasbot succeeded in producing 

 a serous inflammation by the intrapleural injection of very small amounts of the 

 serous exudate from eases of rheumatic pleuritis, while the injection of pure, 

 indifferent fluid had no effect whatever. Duvieusart observed in sheep, shorn 

 during the winter, numerous cases of sickness which began on the second 

 day after shearing; some cases developed even after the animals had been brought 

 to a warm place, proving the infectious nature of the affection. (These were 

 evidently cases of hemorrhagic septicemia.) Imnielmann's observations among lambs 

 were probably of a similar kind (see page 139). There are no more recent reports 

 about pleuritis due to cold (compare the veterinary reports of the Prussian army). 



Influences which weaken the organism, such as overexer- 

 tion, long-continued railroad transportation, etc., predispose 

 animals to infections in general and to pleurisy in particular. 



If there is no disease of any other organ and no general dis- 

 ease which might be the cause of the pleuritis, the latter is des- 

 ignated as a primary pleuritis in contradistinction to secondary 

 pleuritis, which may be referred to another primary disease. 



Anatomical Changes. The acute inflammation begins with 

 an arterial hyperemia and the surface of the pleura simultane- 

 ously becomes rough, lusterless and dry. Blood-plasma is ex- 

 travasated and also a larger or lesser number of white blood 

 corpuscles ; fibrin is deposited in the exudate which covers the 

 surface like a spiderweb or veil, sometimes in somewhat thicker 

 deposits; it is very friable and loosely adherent (pleuritis 

 fibrinosa s. sicca). In other cases, the inflammatory process 

 leads to the formation of an abundant serous and fibrinous ex- 

 udate (pleuritis seroso-fibrinosa). The serous exudate is some- 

 times rather clear, yellowish or reddish, possibly greenish 

 (pi. serosa) ; at other times more or less cloudy, in consequence 

 of suspended flocculi of fibrin and cells ; then the pleura is cov- 

 ered with thicker, friable, moist, loose, yellowish fibrinous 

 membranes. 



The amount of the exudate varies very much. In the pleura of horses one 

 generally finds 15 to 20 liters of fluid, sometimes much less, at other times much 

 more. (Gosier found 60 liters in one case, Holmes 155 pounds of fluid) ; the average 

 amount in dogs is % to 5 liters; in hogs 2 to 10 liters (Friedberger & Frohner). 



The thickness of the fibrinous pseudomenibraue varies between some millimeters 

 to several centimeters. Its surface is generally uneven and villous. In cases with a 

 very rapid course the amount of fluid exudate usually predominates, in protracted 

 cases the amount of fibrin. 



In some cases, the exudate becomes purulent (pi. purulenta 

 s. pyothorax, s. empyema), but it may then also contain 



