158 PHYSIOLOGICAL EEGULATIONS 



of plasma rather than of whole blood, and plasmapheresis (without 

 replacement of anything but corpuscles) rather than hemorrhage. 

 Suitable data of those sorts scarcely exist, unless in dogs subse- 

 quent changes of volumes be inferred from changes of concentra- 

 tion (Weech et al., '33; Calvin et al., '33; Freeman et al., '38). 



In rabbit many independent data confirm the recoveries of 

 ''plasma" and of ''blood" volume above described {e.g., Boycott 

 and Douglas, '09 ; Nagaoka, '36 ; Oka, '38). In dog, man, and other 

 species, partial data are not lacking. Those who are familiar with 

 measurements of "blood" volume each have favorite researches 

 that might be considered in this connection. What I would prefer 

 is a thoroughly systematic study, with estimations of volume at 

 initial intervals of only 0.02 hour, that does not yet exist. 



In a few words, the maintenances of "blood" and "plasma" 

 volumes depend upon net exchanges of those fluids in appropriate 

 directions. After an excess has been established, net loss is rapid 

 and in proportion to the amount of excess. After a deficit has been 

 established, net gain appears. "Plasma" is exchanged faster than 

 blood "cells." Investigations designed to discover machinery by 

 which these compensations operate have succeeded only in confirm- 

 ing these bare facts for a number of diverse types of volume load, 

 and in several species. 



§60. Arm 



The human arm is a suitable unit for measuring volume changes, 

 if by a pressure plethysmograph the volume of tissues minus blood 

 is observed at desired intervals of time. The rates of escape of 

 tissue fluid that had previously accumulated under partial venous 

 stasis are thus ascertained (fig. 97). The rate of decrease of vol- 

 ume in the hydrated arm turns out to be a function of the amount 

 of excess fluid present in it. No methods or data exist to tell 

 whether the gain of volume to an arm previously depleted of some 

 of the usual fluid would likewise be proportional to the deficit. So 

 far as the evidence goes, the "fixed" tissue mass of the arm adjusts 

 its volume after a disturbance of it, in the same manner as the 

 blood of rabbit, or the whole man. 



<§. 61. Other organs 



Some organs of the animal body are geographically available 

 for enclosure in oncometers and plethysmographs. Of the large 



