478 BLOOD AND LYMPH. 



diffusion and osmotic currents. In this way a continual inter- 

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

 is effected, each according to its needs. The details of this inter- 

 change 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 experi- 

 mentally, are simpler, and, as we have seen, are explained satis- 

 factorily by the physical and chemical factore enumerated. 



