Etiology. Anatomical Changes. Symptoms. 177 



Etiology. Hydrotliorax is usually caused by a congestion 

 in the vena cava and its brandies. It is therefore observed in 

 chronic diseases of the lungs ; still more frequently in chronic 

 cardiac diseases and is usualty associated with ascites, hydro- 

 pericardium and anasarca. The affection is similarly developed 

 in compression of the venous trunks (compare compression of 

 the heart in Vol. I). 



A small amount of clear fluid due to cardiac weakness is usually found in 

 the pleural cavity after a prolonged agonal state. 



Hydrotliorax in other cases depends upon general anemia, 

 hydremia, or indirectly upon a long-standing exhausting dis- 

 ease (glanders, renal disease, echinococeus, carcinomatosis, etc.). 

 The effect of substances which are irritating to the capillary 

 walls may play a role in some cases. 



No observations have been made in veterinary medicine to decide whether 

 congestion in the lymphatics, particularly in the thoracic duct, may be the cause 

 of hydrothorax. 



Anatomical Changes. The transudate in the thoracic cavity 

 appears light, or reddish yellow, perfectly clear or slightly 

 turbid; it may contain very fine flocculi of fibrin, occasionally 

 also numerous red blood corpuscles. It contains a considerable 

 amount of albumin; however, the amount of the latter and the 

 specific gravity are less than that of the blood serum. One 

 usually sees few formed elements under the microscope 

 (desquamated, swollen epithelia, a few l}Tnpli corpuscles and 

 erythrocytes and some cells in a condition of fatty degener- 

 ation). The lungs are compressed in proportion to the amount 

 of the transudate ; the pleurse either show no changes at all, or 

 are somewhat thickened or cloudy. Congestion is usually 

 present. 



Symptoms. Hydrothorax usually develops uniformly on 

 both sides and the signs pointing to a collection of fluid in the 

 thoracic cavity (see page 166) are found bilaterally. The other 

 signs, especially those of compression of the lungs, are the 

 same as in serous pleuritis; they develop, however, somewhat 

 more slowly, without fever and without tenderness of the tho- 

 racic wall. The serous fluid easily changes its place and the 

 area of dullness changes with changes in position of the patient; 

 the upper boundary always remains horizontal. The lower 

 portions of the thorax appear wider in the presence of an abun- 

 dant transudate and the movement of the ribs also requires the 

 action of the accessory respiratory muscles. 



The diagnosis depends upon the detection of the primary 

 disease, the presence of other hydropic conditions, the pro- 



Vol. 2-12. 



