ABSORPTION. 213 



stituents. The cause of this increase in both the quantity and quality 

 of the lymph is believed to be an increased activity in the secreting power of 

 the endothelial cells. 



The more recent experiments of Starling indicate that in addition to the 

 difference of pressure between the blood in the capillaries and the lymph in 

 the tissue spaces, a new factor must be considered and that is, the permea- 

 bility of the capillary wall. This he finds to vary considerably in different 

 parts of the vascular apparatus, being greatest in the capillaries of the 

 liver, less in the capillaries of the intestines and least in the capillaries of 

 the extremities. It also varies doubtless in all other situations. The 

 increase in the production of lymph by the injection of peptones, extract of 

 muscles of the leech, the crab, etc., Starling explains by the assumption that 

 these substances alter the properties of the capillary wall and thus increase 

 its permeability. The difference of pressure, therefore, between blood and 

 lymph taken in connection with the degree of permeability of the capillary 

 wall will account for the production of lymph in all regions of the body. 



Another factor which has been invoked to account for the passage of the 

 constituents of lymph through the capillary wall, is an increased concentra- 

 tion of the intercellular lymph, the result of an accumulation of metabolic 

 products, and hence an increase in the osmotic pressure, which would lead 

 to an increase in the passage of the constituents of the blood into the lymph. 

 The activity of a tissue would thus indirectly lead to the formation of 

 lymph. It is possible that all these facts may be otherwise interpreted; 

 the subject is yet a matter of investigation. 



The Functions of Intercellular Lymph. The origin and composition 

 of lymph, its situation and relation to the tissue cells indicate that its func- 

 tion is to provide the tissue cells with those nutritive materials necessary to 

 their growth, repair, and functional activities, and to receive from the tissue 

 cells the waste products of their metabolism prior to their removal by the 

 blood- and lymph- vessels. 



The necessity for the production of lymph becomes apparent when the 

 chemic changes which the tissues undergo at all times are considered. Thus 

 whether in a state of relative rest or in a state of activity, disintegrative 

 changes are constantly taking place and always in direct proportion to the 

 degree and continuance of the activity. If the tissues are to continue in the 

 performance of their customary activities, it is essential that repair and 

 restoration be at once established. This is made possible by the presence 

 of lymph, and by the power which living material possesses of absorbing 

 from the lymph the necessary nutritive materials, of assimilating them and 

 transforming them into material like unto itself and endowing them with 

 its own physiologic properties. 



Coincidently with the loss of nutritive material, the lymph receives the 

 products of the metabolism of the tissues and hence changes in composition. 

 Should this change in composition continue for any length of time, the 

 lymph would lose its restorative character and become destructive to tissue 

 vitality. Therefore it is essential that the nutritive material be renewed as 

 rapidly as consumed and the waste products be carried away as rapidly as 

 produced. Both these conditions are fulfilled by the blood- and lymph- 

 vessels. 



