LYMPH 253 



It has never been shown that a rise in capillary pressure with a 

 normal venous circulation produces an increased flow of lymph. On 

 the contrary, experiments show that such a rise of capillary pressure 

 may take place without an increased flow of lymph necessarily re- 

 sulting. Reference, for example, has already been made to the 

 fact that stimulation of the chorda tympani causes a great flow 

 of saliva accompanied by a marked flow of lymph from the gland. 

 When the endings of this secretory nerve are paralyzed by atropine, 

 stimulation still produces a marked rise of capillary pressure, but no 

 salivary secretion or increased lymph flow results. So, too, if the 

 motor nerves to a limb be cut, and the blood-pressure raised by causing 

 a general vaso -constriction of the rest of the body, the quantity of 

 lymph flowing from the limb while performing passive rhythmical 

 movements is not increased, but diminished. 



Differences in the constitution of lymph coming from different parts, 

 or from the same part at different times, are attributed upon the 

 filtration view to an altered permeability of the vessel wall. The 

 exact reason for such alterations appears to be due rather to the different 

 forms of activity in the various parts, and in the same parts at different 

 times. Reasons for a disbelief in the possibility of a filtration mechan- 

 ism within the body are adduced in dealing with the capillary pressure 

 (see p. 223). 



Furthermore, it has been shown recently that venous stasis causes 

 lymph formation, not by virtue of filtration, but by changes in the 

 tissues themselves, due primarily to lack of oxygen, causing the forma- 

 tion of acid. With such acid formation, water passes by imbibition 

 into the tissues, leading, if long continued, to oedema. Such a con- 

 dition is pathological, not physiological. 



In regard to the part played by osmosis, it may quite well be that 

 the interchange between blood and tissues is largely regulated by this 

 process. For example, the lymph formation attending tissue activity 

 may possibly be explained by the supposition that the products of 

 cell activity, being relatively of small molecular weight, cause by 

 increased osmotic pressure a flow of fluid from the blood into the 

 tissue spaces. 



The numerous experiments which have been made of injecting 

 such crystalloid bodies as sodium chloride, dextrose, urea, so-called 

 lymphagogues, tend to support the view that osmosis plays a part in 

 the formation of lymph. Certain recent experiments, however, show 

 that the chloride content of the lymph may rise above that of the 

 blood-serum. If this be the case, then osmosis cannot be the whole 

 story. 



It has also been pointed out that each tissue or organ obtains its 

 own special products from the lymph, often in large quantities. The 

 most -quo ted example is the calcium content of milk. A cow may yield 

 daily 25 litres of milk containing 42-5 grammes of Ca. As the lymph 

 of the thoracic duct contains but 0-18 per cent., 236 litres of lymph 

 would be needed to supply this calcium to the milk, assuming that 

 all the calcium comes from the lymph. This is held greatly to support 



