TRANSACTIONS OF SECTION I. 811 



itself in an increased flow from tlie lymphatics, because it was in part stored up in 

 the tissues as oedema fluid. To determine this point observations of the specific 

 gravities of arterial blood and blood-plasraa, venous blood and blood-plasma, of 

 muscle and of skin were taken before and after the pressure in the femoral vein 

 was raised. It was found that these underwent no changes whatever, either in 

 the att'ected limb or in other parts of the body (with the exception of a rise ia 

 the specific gravity of the venous blood and blood-plasma in the afi'ected limb) 

 during venous obstruction, which caused a rise of pressure in the i'emoral vein, 

 varying in individual cases from 48-75 mm. of mercury. The modiflcation of 

 specific gravity of the venous blood and blood-plasma in the affected limb manifestly 

 depends upon its lengthened sojourn in the limb. 



The author concludes, therefore, that increase of venous pressure in a limb for 

 one hour not only does not cause an increase of lymph-flow from the lymphatics, 

 it does not even cause an increased passage of fluid through the blood-vessel walls. 



Independenth', however, of the venous pressure, the amount of lymph-flow is 

 increased wlien the tissues have been starved for some time or are overstocked 

 with their own katabolic products. 



The following conditions were investigated : — 



1. Before and after prolonged complete auaimia (three hours), produced by an 

 Esmarch's bandage. 



2. Before and after hsemostasis, or complete cutting off of the limb, with what- 

 ever blood and lymph it might contain, from the rest of the body by means of a 

 tight elastic bandage for one hour. 



3. Before and after stimulation of the sciatic nerve, while the limb was com- 

 pletely anaemic and persistence in situ of the katabolic products, the whole lasting 

 one hour. 



All these conditions are followed by arterial dilatation in the part ; and^ 

 inasmuch as arterial dilatation subsequent to section of the sciatic nerve was found 

 by the author to be unaccompanied by any modification in the amount of lymph- 

 flow, he concludes that the increase occurring under the conditions given above is 

 immediately conditioned by the excessive needs of the tissues. 



Under extreme conditions, such as those just given, the eflect of an increase of 

 venous pressure is markedly difi'erent from what it is when such conditions have 

 not been introduced, for now an increase of venous pressure is accompanied by an 

 increase in the lymph-flow, while the lymph-flow diminishes when the venous 

 pressure is again allowed to return to normal. In other words, the lymph-flow 

 now varies directly — the author cannot say whether it be proportionately — with 

 the venous pressure. It now, therefore, bears some resemblance to mechanical 

 filtration. Inasmuch, however, as an obstruction to the outflow of blood from the 

 venous side itself intensities the necessity of the tissues by damming up in them 

 the waste products they are so anxious to get rid of, this resemblance to mechanical 

 filtration may, after all, be only apparent. 



The author concludes, therefore, that lymph-formation does not depend upon 

 purely mechanical conditions of the circulation, but he regards it as dependent 

 upon the needs of the tissues: those needs are, in some as yet unrecognised way, 

 made known to the circulatory apparatus, and lead to variations in tlie amount of 

 blood-flow through the part, in extreme cases active arterial dilatation of the most 

 marked kind being induced. In such extreme cases, further, the lymph-flow 

 varies directly with the A-enous pressure, and there is a resemblance to mechanical 

 filtration; but there are reasons for supposing that this resemblance is an apparent 

 and not a real one. 



3. On the Innervation of the Portal Vein. 

 By W. M. Bayliss and Dr. Starling. 



4. On some Vaso-dilator Reflexes. By W. M. Bayliss. 



