354 PHYSIOLOGICAL EEGULATIONS 



ery of cardiac output (fig. 176) after a certain intensity of exercise, 

 appears to occur in the first half minute with a velocity quotient of 

 75/hour. Hence the tolerance curve for presumed cardiac output 

 or rate of total blood flow, is similar to that for heart frequency and 

 to that for systolic arterial pressure. 



When cardiac output is divided by frequency of heart beats, 

 values for ' ' stroke volume ' ' are obtained. ' ' Stroke volume ' ' shows 

 approximately the same deceleration as the above quantities. Or, 

 by multiplying cardiac output by oxygen delivered per heart beat 

 C oxygen pulse"), values for rate of oxygen consumption are ob- 

 tained. Altogether, three more quantities are thus added to the 

 group of recoveries measured in the one experiment of figure 176. 



Constancy of convection is secured by a variety of self -induced 

 modifications in the vascular apparatus. Failure of blood or of 

 some of its components to arrive in the usual amount in a given 

 tissue mass, is followed by conpensatory increases of blood flow 

 (''reactive hyperemia"). These are adequately seen in the 

 sequelae of partial arterial occlusion (Rein and Schneider, '37). 

 Flow of blood in excess of the mean rate also appears to be com- 

 pensated equally promptly; perhaps the regulation is one of suf- 

 ficiency rather than of opposition to excess. 



The same investigators ( '30, p. 264) were actually able to dem- 

 onstrate that during acceleration of flow to a muscle that was stimu- 

 lated by electrical shocks to appropriate nerves in an anesthetized 

 dog, the arterial inflow exceeds the venous outflow, and during 

 deceleration vice versa. Hence a charge or load of blood fills the 

 widened blood vessels as long as the greater blood flow lasts. 

 Recovery (deceleration) of local flow, like the recovery of so many 

 diverse components, is then related to this measured load or excess. 



§ 127. Regeneration of tissue 



(1) Tadpole tail. Experiment consists in removal of diverse 

 amounts of tissue, after which the rate of tissue replacement may be 

 measured. From the large number of studies in which partial 

 information has been gained, I select the data of Zeleny ( '16) upon 

 the tails of tadpoles of Rana clamitans. Amounts of bodily mate- 

 rial removed are ascertained in terms of linear length, the whole 

 tail's length being taken as 100 per cent. The tissues replaced 

 may or may not have the same proportions, compositions, or 

 anatomical elements as those removed. 



