THE FORMATION OF LYMPH. 413 



from the blood into the lymph spaces, and when there 

 attract water from the tissues. Long-continued obstruction 

 of the aorta does not annul their action. When the aorta 

 is closed for over an hour, injection of crab extract fails to 

 produce a formation or secretion of lymph; but thirty or forty 

 grains of sugar cause at once an increased lymph stream. 



From these experiments, Heidenhain distinguishes 

 between the two kinds of lymph, "blood lymph" and 

 "tissue lymph"; he regards the capillary wall not merely as 

 a passive membrane or filter, but one capable of exerting 

 secretory or selective activity, just as the renal epithelium 

 selects from the blood the materials it pours into the urine. 

 This secretory action is stimulated by the substances 

 included in his first class of lymphagogues. He, moreover, 

 points out that the outflow of lymph from the thoracic duct 

 is nearly the same whether the aortic pressure is 10 or 

 100-200 mm. of mercury, and so blood-pressure cannot be 

 an important factor in lymph formation ; and though he 

 admits that in venous obstruction an outflow of fluid takes 

 place as a result of filtration, yet he considers in the normal 

 condition filtration plays no part whatever. This view he 

 founds chiefly on the action of his lymphagogues, which 

 increase the amount of lymph to a marvellous degree, 

 without a corresponding alteration in arterial blood pressure, 

 and the chemical composition of the lymph so formed is 

 incompatible with any mechanical theory ; for instance, after 

 the injection of sugar, the percentage of sugar in the lymph 

 rises considerably over that in the blood. 



Such then are the main features of a piece of work 

 which has, during the last few years, exercised such a 

 profound influence on the conceptions of modern physiology. 



As previously stated, it will be my duty in conclusion 

 to give a resume of the work which Starling has done, and 

 which has led him to oppose Heidenhain's conclusions. The 

 papers he has written are four in number, and they have all 

 been published in the Journal of Physiology} 



1 Vol. xiv., p. 131 ; vol. xvi. (with W. M. Bayliss), p. 159 ; vol. xvi., 

 p. 224 ; vol xvii., p. 30. 



