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NUTRITIONAL PHYSIOLOGY 



nally, to make the correspondence closer, assume that the 

 faucets can never be shut tight (for it is not likely that the 

 blood-vessels can be). Now, by manipulating the cock 

 (H) we can increase or diminish the outflow into all the 

 tubs, but we cannot in this way hasten the filling of one 

 more than another. This is obviously the type of cardiac 

 regulation in the living system. The heart is appealed to 



Fig. 23. The supply, to all the tubs is controlled at the " shut 

 off " ( H), while the share flowing into each compartment is regulated 

 by its own faucet (F). 



when there is a general and widespread demand for more 

 blood per unit of time, muscular activity being by far the 

 most important occasion. 



The faucets over the several tubs 'are the symbols of 

 vasomotor equipment. By using them we can change the 

 share of the total stream which shall enter any compart- 

 ment. If our only desire is to fill one tub, we can open 

 widely that faucet and close the others as far as possible. 

 The vasomotor system actually operates in that way to the 



