182 THE FLUIDS. 



this head ; and the hydragogue effects (so called) of certain cathar- 

 tics. 1 



Transudation results, as a physical necessity, whenever bloodvessels 

 are exposed very near to a surface in contact with the air, as is the 

 case with the air-passages and the skin. But the state of fulness of 

 the vessels, and the rapidity of the circulation through them, as 

 well as the physical and chemical character of the blood itself, also 

 exert a controlling influence on the amount of fluid transuded. The 

 fuller the vessels, and the slower the motion of the blood-current, 

 the greater is its amount. Hence congestion of the vessels of a 

 part is a common cause of transudations ; e. g. diarrhoea from portal 

 congestion. And since congestion is often produced by pressure 

 on venous trunks, the latter is commonly accompanied by oedema, 

 anasarca, or ascites ; as, in case of the last, from abdominal tumors, 

 ovarian or otherwise. That the accumulation in such cases is not 

 secretion merely, is evidenced by the fact that it amounts in some 

 instances to 2 or even 3 pounds per day. 



Transudations, like serous secretions, very nearly resemble the 

 blood-serum in chemical composition, and, like them, they also nor- 

 mally contain no fibrine. But since animal membranes are more 

 easily penetrated by water than by the other constituents of the 

 blood-serum, next by the extractive matter and soluble salts, and 

 then by albumen, it follows that trausudations will contain more 

 water proportionally to the solids than blood-serum does, and more 

 salts in proportion to their albumen. 



The quantity of albumen in transudations varies exceedingly. 

 Lehmann states that it mainly depends on the following circum- 

 stances : 



1. Certain systems of capillaries transude more than others; e.g. 

 those of the pleura most of all, and those of the ventricles of the 

 brain least of all. 



2. The slower the blood-current in the capillaries, the richer in 

 albumen is the transudation ; e. g. more albumen is found in peri- 

 toneal transudations (ascites) when dependent on pressure from 

 large tumors than when caused by less disturbance of the circula- 

 tion, as by cirrhosis of the liver. 



3. The poorer the blood is in albumen, the less appears in transu- 



1 Lehmann also adds hydatids, and vesicular eruptions on the skin from any 

 cause, to this list. 



