THE CIRCULATION AND CIRCULATION RESEARCH IN PERSPECTIVE 



emphasis is given to mechanisms of blood supply 

 that can be only temporary emergency mechanisms. 

 Accepting current estimates that the ventricles con- 

 tain residual volumes that may exceed those ejected, 

 and that the pulmonary venous system also constitutes 

 a reservoir of blood, my calculations indicate that 

 the total cardiopulmonary reserve can be pumped 

 out within 5 or 6 sec after the onset of strenuous exer- 

 cise. Tliereafter, augmented cardiac output can be 

 maintained only by a corresponding increase in 

 venous return. 



Despite man\' earnest efforts to elucidate the 

 sources of additional venous blood and the mecha- 

 nisms bv which v^enous return is augmented (5, 22, 

 26, 31, 41), most of the conclusions are based on 

 inferences and extrapolations rather than on direct 

 experimental evidence. Hence the study of veno- 

 pressor mechanisms remains a promisina; field for 

 future investigations. 



A few words in conclusion : the reader may infer 

 that the author of this chapter has reached an age 

 when the tendency to recall significant advances of 

 the past exceeds his capacity to appreciate the full 

 value of contemporaneous ones. They may be re- 

 assured however that he had no intention of down- 

 grading the highly significant contributions of the 

 present generation of active workers. Since these new 

 advances will be stressed predominantly in subsequent 

 chapters, it seemed appropriate to recall that the 

 scholarly assessment of current work also requires 

 recognition of accomplishments of the past and some 

 knowledge of the underlying reasons for frequently 

 changing points of view. Research, as the word im- 

 plies, consists in searching again and again to make 

 quite certain that propositions regarded as estab- 

 lished are indeed true. A historical perspective teaches 

 us not to repeat investigations made by simpler means 

 too often, just because more complicated methods 

 have become available. 



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