COMPOSITION AND FORMATION OF LYMPH. 477 



seriously alter general arterial pressure, they may greatly augment 

 intracapillary pressure, particularly in the abdominal organs. His 

 explanation of the greater flow of lymph in these cases is as follows : 

 " On their injection into the blood the osmotic pressure of the circu- 

 lating fluid is largely increased. In consequence of this increase 

 water is attracted from lymph and tissues into the blood by a process 

 of osmosis, until the osmotic pressure of the circulating fluid is 

 restored to normal. A condition of hydremic plethora is thereby 

 produced, attended with a rise 6f pressure in the capillaries generally, 

 especially in those of the abdominal viscera. This rise of pressure 

 will be proportional to the increase in the volume of the blood, and 

 therefore to the osmotic pressure of the solutions injected. The 

 rise of capillary pressure causes great increase in the transudation 

 of fluid from the capillaries, and therefore in the lymph-flow from 

 the thoracic duct." This explanation is well supported by experi- 

 ments, and seems to obviate the necessity of assuming a secretory 

 action on the part of the capillary walls. 



5. Numerous other experiments have been devised by Heidenhain 

 and his followers to show that the physical laws of filtration, diffu- 

 sion, and osmosis do not suffice to explain the production of lymph ; 

 but in all these cases possible explanations have been suggested 

 in terms of the physical laws, so that it may be said that the 

 facts do not compel us to assume a secretory activity on the 

 part of the endothelial cells of the capillaries. Asher* and his 

 co-workers have brought forward many facts to show that the lymph 

 is controlled as to its amount by the activity of the tissue elements 

 and may be considered as a product of the activity of the tissues, as 

 a secretion, in fact, of the working cells. When the salivary glands, 

 the liver, etc., are in greater functional activity the flow of lymph 

 from them is increased beyond doubt, so that the activity of the 

 organs does influence most markedly the production of lymph. 

 Most physiologists, however, prefer to explain this relationship on 

 the view suggested by Koranyi, Starling, and others, namely, that 

 in the metabolic changes of functional activity the large molecules 

 of protein, fat, etc., are broken down to a number of simpler ones, 

 the number of particles in solution is increased and therefore the 

 osmotic pressure is increased. According to most observers 

 the molecular concentration of the lymph in the thoracic duct, 

 and, therefore, the osmotic pressure, is greater than that of the 

 blood. Thus Botazzi,f in one experiment, reports that the 

 lowering of the freezing-point of the blood-serum was A =0.595 

 C., while that of the lymph from the thoracic duct of the same 



* "Zeitschrift f. Biologic, " vols. xxxvi-xl, 1897 to 1900. 

 t Quoted from Magnus, "Hahdbuch der Biochemie," 1908, vol. ii. 2 (For- 

 mation of Lymph). 



