522 PHYSIOLOGY CHAP. 



current. The following are the facts which bear upon this pro- 

 position : 



(a) When in a dog all the cervical and brachial nerves to an 

 anterior limb are divided so as to paralyse all motor nerves to the 

 muscles as well as the vessels, and the cervical cord is stimulated 

 electrically so as to produce contraction of all the vessels of the 

 body except those of this limb, there is necessarily a marked efflux 

 of blood with increased arterial and capillary pressure in all the 

 vessels of the paralysed limb. Nevertheless the quantity of lymph 

 flowing with the aid of the passive, rhythmical movements of the 

 limb from the cannula inserted into its lymphatic trunk does not 

 show the slightest augmentation, but rather tends to diminish 

 gradually, as it did previous to stimulation of the spinal cord 

 (Ludwig and Paschutin). 



(&) When the so-called chorda tympani is excited there is a 

 conspicuous dilatation of the small arteries of the subniaxillary 

 gland, associated with increase of pressure and acceleration of 

 the blood-flow through the capillaries (Chap. X. 1, p. 341). These 

 effects are certainly associated with increased formation of lymph, 

 which pours into the glandular lymphatic spaces, and (as we 

 shall see, Vol. IT. Chap. II.) is immediately utilised by the gland 

 cells for the formation of an abundant salivary secretion 

 (Ludwig), so that it does not accumulate in the glandular 

 lymphatics. If, before exciting the chorda tympani, the animal is 

 slightly atropinised, the vessels of the gland will equally dilate, 

 and capillary pressure rises as before; but the salivary secretion 

 does not occur, nor is there any increased formation of lymph, 

 since it does not accumulate in the connective-tissue spaces of the 

 gland, nor does the flow of lymph from the glandular lymphatics 

 increase (Heidenhain). To interpret this effect we must remember 

 that atropine paralyses the activity of the secretory nerves, leaving 

 the vasodilator fibres of the chorda tympani untouched. Mere 

 arterial dilatation and rise of pressure and circulatory velocity in 

 the capillaries of the gland are not enough to provoke increased 

 formation of lymph, such as does, on the other hand, occur 

 when the secretory activity of the gland cells are excited. 



These facts are obviously irreconcilable with the theory that a 

 primary importance must be assigned to the mechanical process of 

 filtration in the physiological formation of lymph. They prove 

 that when the increased pressure in the blood capillaries is 

 associated with acceleration, instead of with slowing or stasis of 

 the circulatory current, no increased formation of lymph takes 

 place. 



Another important series of experimental observations shows 

 that the lymph current may increase conspicuously, independent 

 of any marked rise in pressure in the blood capillaries : 



(a) Certain chemical substances, when injected into the blood, 



