1894.] the (Edema ivhich accompanies Passive Congestion. 63 



He estimates the occurrence or non-occurrence of oedema by the 

 speci6c gravity of the blood and blood-plasma, arterial and venous, 

 of mnscle and of skin, regarding these aa more delicate tests of the 

 presence or absence of oedema than the rougher methods of inspec- 

 tion, measurement, and pitting on pressure. 



Having raised the pressure in the femoral vein to 50 mm. of 

 mercury, he finds that there is no alteration in the specific gravity of 

 the blood or blood-plasma of the muscle or of the skin, nor is 

 there any increase in the amount of the lymph-flow, though such a 

 pressure be maintained constant for an hour. 



In the affected limb only is any change to be noted, and here there 

 s a rise in the specific gravity of the venous blood and blood-plasma, 

 which depends upon the longer sojourn of the blood in the limb and 

 the consequent greater removal of the more watery portion from a 

 given volume of blood. 



Inasmuch as it is essential upon a purely mechanical explanation 

 that the exudation from the blood-vessels should be increased in 

 amount synchronously with the increase of pressure, and no such 

 exudation is found to take place during an hour after the pressure 

 in the veins has been raised, the author considers that the mechanical 

 explanation is not supported by facts. 



Since all forms of oedema are accompanied by an insufficient supply 

 of blood to meet the requirements of the tissues, the author investi- 

 gated the effect of different varieties of anaemia upon the occurrence 

 of oedema. The varieties investigated were : 



1. Prolonged complete anaemia, lasting three hours. 



2. Hsemostasis, or cutting-off of the limb, with whatever blood 



and lymph it may contain, from the rest of the circulation, 

 by means of a tight ligature, for one hour. 



3. Complete anaemia combined with stimulation of the sciatic 



nerve, and persistence, in situ, of the products of muscle- 

 metabolism, the whole lasting one hour. 



After each of these three varieties of anaamia the effects of active 

 congestion, and of venous obstruction, were separately considered. 



It was found that oedema occurs, as shown by a fall in the 

 specific gravity of the muscle and skin, and a rise in the specific 

 gravity of the blood, after all these conditions of anaemia, and the 

 author concludes, therefore, that starvation of the tissues plays an 

 important part in the occurrence of oedema. 



The amount of oedema obtained, however, was found to be greater 

 in those cases in which the limb had been subjected to the action of 

 venous blood, and the longer the action of the venous blood was 

 allowed to obtain, the greater the amount of oedema. The author 

 concludes that the presence of the products of tissue metabolism at 



