166 



PHYSIOLOGICAL REGULATIONS 



lar units in general, either the whole cell may be concerned in giving 

 up excessive water, or special structures like vacuoles may segre- 

 gate that water, and either the whole cell or its surface may in 

 deficits take up water. Both exchanges may represent special 

 arrangements for regulatory water contents. 



§ 67. Summary 



How water is handled by living units, is ascertained in parts of 

 organisms in which the volumes can be measured. Volume changes 

 are treated as net changes of water content. Both volume and 

 water content suffer increments of many measurable types, each 

 representing one method of loading the living unit. 



In all the tissue masses or cells that have been studied under 

 conditions appropriate for recovery toward balance of volume (as 

 defined previously, '§19), initial exchanges are faster as the incre- 

 ments are larger. The directions of the exchange of fluid are such 

 as to restore the masses to the volumes characteristic of control 

 masses. I conclude that portions of individuals show much the 

 same pattern of net compensations that whole organisms do. 



Comparisons of exchanges by the diverse tissues and cells 

 studied (table 8) are limited by the less accuracy of the data as com- 



TABLE 8 

 Comparisons among net recoveries of water content or volume in tissues and cells 



pared with those in whole organisms. It is clear that the most 

 rapid recovery is in the smallest living unit, the leucocyte. Veloc- 

 ity quotients indicate that exchanges between plasma and the re- 



