EQUILIBKATIONS IN PAETS OF ORGANISMS 161 



"blood" volumes. By transformation of coordinates, net equili- 

 bration diagrams are obtained for these volumes. Certain experi- 

 mental "injuries" to the rabbits modify significantly the rates of 

 plasma exchange, possibly indicating what sites or intermediaries 

 take part in the exchanges. In studies by direct mechanical or 

 optical measurements, volume changes are ascertained in arm, in 

 certain distinct organs, in cells, and in their subdivisions. Only for 

 blood and for arm are concrete portions of the equilibration dia- 

 gram definitely established. 



§ 64. Isolated parts 



Another large field in the investigation of equilibrations of vol- 

 umes lies in isolated parts of organisms. These parts may be 

 living or dead, or both, according to diverse criteria that are arbi- 

 trarily chosen; for, survival after isolation is inevitably a matter 

 of definition. 



In general the increments of volume whose recovery is to be 

 studied may be established (d) before isolation, or (e) after isola- 

 tion. Thus (d), a dog or a frog may be loaded with water, and 

 then its tissues may be isolated and allowed to equilibrate by ex- 

 changing fluid with a selected medium. Or (e) the tissues or cells 

 may be removed from the body while in water balance, thereafter 

 loaded and then transferred into the standard medium for equili- 

 bration. 



Blood or plasma, being liquid, might be studied under isolation 

 by putting samples of either behind uniform or identical partitions 

 of some natural or artificial membrane. While the samples are ex- 

 changing water with large volumes of a selected liquid, the rates of 

 transfer would be measured. Other body fluids may be studied in 

 like fashion. In any isolated units, the number of arbitrarily 

 chosen factors will be much larger than within the intact body 

 where these factors are already fixed by the organism. One or 

 another of those factors will seem to someone to be "unphysio- 

 logical. ' ' 



§ 65. Isolated muscles 



Muscles isolated from frogs are studied by both method (d) and 

 method (e). Positive loads are produced by injecting water intra- 

 peritoneally and allowing either 0.5 or 1.7 hours for the water to 

 distribute itself; then the muscles are isolated (method d) and 



