332 EDEMA 



in proportion to blood pressure, etc. If in glandular secretion, there- 

 fore, fluids are removed from the blood and transferred into an ex- 

 cretory duct through the action of some force other than that of the 

 blood pressure, it is probable that lymph formation is equally inde- 

 pendent of blood pressure. On this basis Heidenhain advanced 

 his — 



Secretory theory of lymph formation, in which he suggested that 

 lymph is the product of an active secretion by the endothelial cells 

 of the capillaries, just as saliva is the product of the activity of the 

 glandular cells. He showed that certain chemical substances may 

 stimulate lymph flow, independent of blood pressure, just as pilocar- 

 pine and other drugs may stimulate the secretion of saliva. These 

 lymph-stimulating substances, which he named lymphagogues, fall into 

 two distinct classes. One which includes such substances as peptone, 

 leech extract, strawberry juice, extracts of crayfish, mussel or oysters, 

 and numerous other tissue extracts, are characterized by causing the 

 secretion of a lymph which is rich in proteins, even richer in proteins 

 than the blood plasma; and, furthermore, there is no simultaneous 

 increase in urinary secretion. Heidenhain considered that these sub- 

 stances caused lymph secretion by stimulating the capillary endothe- 

 hum in a specific manner; as they caused no appreciable rise in blood 

 pressure the increased lymph secretion certainly could not be attrib- 

 uted to filtration. This independence of the lymph flow of blood 

 pressure is most conclusively shown by posttriortem lymph secretion; 

 for example, Mendel and Hooker'* observed lymph flow for four hours 

 after death, in a dog that had received an injection of peptone eight 

 minutes before being killed.^ 



The second class of lymphagogues includes crystalloidal substances, 

 such as sugar, urea, and salts. ^ Lymph secreted under the influence 

 of these substances is poorer in protein than ordinary h'mph, and at 

 the same time an increased urinary secretion is produced. With 

 these crystalloidal lymphagogues the amount of effect is in inverse 

 proportion to their molecular weight, which means that their effects 

 depend upon the number of molecules in solution rather than upon 

 their nature; in other words, the stimulation of Ij^mph by crystalloids 

 is dependent upon the osmotic pressure of the crj'stalloids. Heiden- 

 hain explained their action as follows: The crystalloids are secreted 

 into the lymph-spaces by the action of the capillary endothelium, and 

 there, owing to their raising osmotic pressure, cause a flowing of 

 water out of the vessels. The difficulty here is to explain why the 

 crystalloids while still in the vessels do not attract the fluids from 



* Amer. Jour, of Physiol., 1902 (7), 380. 



' A fact not sufficiently taken into account is that blisters filled with serum, 

 i. e., an inflaniinatory edema, may be produced in dead bodies bv liurns or scalds. 

 (See Leers and Raysky, Virchow's, Arcli., 1909 (197), 324). 



* The action of many other substances has been investigated bv Vanagawa, 

 Jour. Pharmacol., 191() (9), 75. 



