468 FORMATION OF LYMPH 



aquatic birds erection is due to the filling of the corpus cavernosum, 

 not with blood, but with lymph. The lymph is secreted rapidly by 

 the so-called bodies of Tannenberg when certain sympathetic nerve- 

 fibres are experimentally stimulated, and passes into the corpus 

 cavernosum, which swells up. If a small incision is made in the 

 corpus, a large quantity of clear lymph, which clots slowly on stand- 

 ing, escapes. There is a simultaneous vasodilatation. After erection, 

 the lymph is rapidly and completely reabsorbed (Eckhard, Miiller). 



Although no definite lymph-secretory nerve-fibres have as yet 

 been discovered in mammals and for ordinary tissues, it is possible 

 that they exist (Sihler). As already pointed out, the same volume 

 of liquid as escapes into the ducts of the active submaxillary gland 

 must, upon the whole, pass out of the blood capillaries. On what 

 principle shall we distinguish one only of these processes as physio- 

 logical secretion ? They begin together when the chorda tympani 

 is stimulated. A drug which paralyzes secretory nerve-endings 

 abolishes both effects. The simplest explanation is that the chorda 

 contains secretory fibres which influence the formation both of 

 saliva and of the tissue liquid from which it is recruited; and, so 

 far as this consideration goes, it is just as logical to consider the 

 increase in the supply of tissue liquid as the cause of the increase 

 in the flow of saliva as to consider the increased salivary secretion 

 as the cause of the increased flow of liquid into the tissue spaces. 

 The increased flow of liquid may be brought about either by an 

 action of the nerve on the gland-cells, causing them to produce a 

 hormone, which then effects the blood capillaries (Carlson), or by 

 a direct action on the capillary endothelium. The advantage to 

 cells engaged in the active secretion of saliva of being immersed in 

 an abundant bath of tissue liquid is obvious. 



The post-mortem flow of lymph, which may continue in some 

 cases long after complete cessation of the circulation for an hour 

 after injection of dextrose to produce hydraemic plethora; for as 

 much as four hours after injection of extract of the strawberry, 

 which is a lymphagogue of Heidenhain's first group (Mendel and 

 Hooker) is a phenomenon whose relation to normal lymph forma- 

 tion has not been definitely settled. 



It ought to be remembered in this whole discussion that the 

 epithelium of ordinary glands derives its supplies of material from 

 the tissue lymph. The vicissitudes of blood-pressure affect it only 

 in a secondary and indirect manner. On the other hand, the endo- 

 thelial cells of the capillaries are in direct confact with the blood. 

 And it is interesting to observe that in this respect the glomeruli 

 of the kidney and the alveoli of the lungs (if the endotheliaUining 

 of Bowman's capsule and the alveolar membrane are assumed to 

 be complete) take a middle place between the glands proper and 

 the quasi-glandular capillaries. 



