480 BLOOD AND LYMPH. 



From the foregoing considerations it is evident that changes 

 in capillary pressure, however produced, may alter the flow of 

 lymph from the blood-vessels to the tissues, by increasing or 

 decreasing, as the case may be, the amount of nitration; changes in 

 the composition of the blood, such as follow periods of digestion, 

 will cause diffusion and osmotic streams tending to equalize the 

 composition of blood and lymph; and changes in the tissues them- 

 selves following upon physiological or pathological activity will 

 also disturb the equilibrium of composition, and, therefore, set up 

 diffusion and osmotic currents. In this way a continual interchange 

 is taking place by means of which the nutrition of the tissues is 

 effected, each according to its needs. The details of this interchange 

 must of necessity be very complex when we consider the possibilities 

 of local effects in different parts of the body. The total effects of 

 general changes, such as may be produced experimentally, are 

 simpler, and, as we have seen, are explained satisfactorily by the 

 physical and chemical factors enumerated. 



