130 



PHYSIOLOGICAL EEGULATIONS 



after each period begins. In 215 such readings each rat tested 

 spent most time in moister air. Since the animal is nearly always 

 found at one end of the box or the other, the data are most readily 

 analyzed in terms of frequencies in two locations. Only rarely does 

 an individual stay at intermediate portions of the long box; but 

 occasionally (fig. 78) a high humidity even in the center of the box 

 is preferred to the otherwise more attractive ends. 



When rats are previously in water deficits of diverse extents, 

 established through privation of water but not of food, they fre- 

 quent moist air more often than when they are in water balance 

 (fig. 79). In extreme deficits of body weight thus induced (AW - 25 



rt 



.2 If 



^ 11 



If : I 



r 



4 

 Hours 



8 



Fig. 78. Position of rat in boxes containing moist and dry air, in relation to time. 

 Location of air of highest humidity is shown by dotted lines; location of rat is shown 

 by continuous line. In A, rat R (AW -26) was in the long box. In B, rat L (AW -35) 

 was in the two-chamber apparatus during two successive days, remaining in the right 

 chamber overnight. New data. 



to -32) the preferences are almost invariable, though in certain 

 few tests the same animals appear to be indifferent to humidity. 

 The correlation of position of rat with water load is statistically 

 significant. The correlation clearly belongs to the category of regu- 

 lations, for in deficits of water the rat avoids atmospheres in which 

 evaporation is faster. 



Having found that rats spend most time in one end or other of 

 the long box, with infrequent tours between them, I used a second 

 apparatus consisting of two chambers connected by a tunnel. The 

 chambers being suspended, positions of the rat could be automati- 

 cally recorded. In them a stream of moist air displaces dry air 

 within 0.2 hour and correspondingly the rat shifts its position more 



