METABOLISM AND THE DISTRIBUTION OF MATERIAL 223 



results in their swelling or edema. We recognize from this, that the 

 dynamic balance of the swelling is dependent upon the normal 

 course of the processes of assimilation and dissimilation. Con- 

 versely, pathological processes are always followed by an abnormal 

 condition of swelling. 



Pathology of Water Distribution. 



In pathological conditions, the water content may have values 

 very different from normal. The water in the blood rises to 90 per 

 cent and more in severe anemias, and may fall to from 73.2 to 66.5 

 per cent in diabetes (see p. 219). Under other pathological condi- 

 tions, organs may show abnormal swelling (see last column in Table 

 III, p. 219). 



With the active metabolism and formation of crystalloids, which 

 occur in fever, there are alterations in swelling (thirst, dryness of 

 the skin), the exact nature of which we do not as yet understand. 



As a rule, there has been less attention paid to the study of the 

 conditions in which the swelling of an organ is below normal. The 

 injection of protoplasmic poisons (some heavy metal salts, strong 

 acids) causes a coagulation of the organ albumen, which reduces to a 

 greater or less extent its swelling capacity. I am still occupied with 

 more exhaustive studies of these questions which are also touched 

 upon in the chapter on Necrosis. It is too early to report the 

 results. 



Edema. 



By edema we understand an abnormal collection of fluid in tissue 

 or tissue spaces; if the fluid collects abnormally in a body cavity, we 

 call it an exudate or hydrops. 



The view most generally accepted up to a few years ago was that 

 edema occurred whenever the venous blood pressure, or more cor- 

 rectly, the difference between arterial and venous pressure was gen- 

 erally or locally raised, and the resistance of the vessel walls was 

 diminished (JULIUS COHNHEIM, 1877). It is known that in heart 

 disease and hi nephritis, when the circulation is disturbed, that large 

 portions of the body, especially the lower extremities, swell and 

 become edematous. The local inflammatory edema accompanying 

 inflammation, insect bites or the injection of an irritating fluid (e.g., 

 diphtheria toxin) must also be considered. 



The above explanation has some fascination, and it cannot be 

 denied that it will continue to be invoked in explanation of certain 

 points, especially since the observation of increase in the permeability 

 of vessel walls cannot be avoided, when we see that even corpuscles 



