general featuees of water exchanges 177 



§ 71. Time relations 



What can be learned by analyzing the time relations in re- 

 sponses to sudden water increments? Initiation of response to 

 load, signalized by acceleration of exchange, is (table 14) without 

 measurable lag in water deficits of all species. In water excesses 

 the responses are more diverse, they appear to begin most 

 promptly where osmosis gives direct passage of water to and from 

 the aqueous environment. Where fluids are excreted by recog- 

 nized special organs, a few species as frog and Rhodnius appear 

 to accelerate elimination without lag; actually there is a lag, of 

 probable significance (0.04 hour), even in the frog's diuresis 

 (Adolph, '36a). It is possible to guess the extended lag in mam- 

 mals is a period in which fluid becomes preferentially distributed 

 to tissues before much escapes from the body. 



The maximal response (rate) is achieved almost instantly in 

 several species, especially in acceleration of intake. Where this is 

 the case, time is probably not a distinct factor in the exchanges, 

 except as the loads or other quantities change with time. 



Completion of recovery, just like the initiation and the maximal 

 stage of recovery, is related to the load of water administered. 

 One criterion of completion (table 14) is the state existing when 

 the rate of exchanges has returned to within ± 30 per cent (see 

 table 12) of the initial or the control rate; this defines the end of 

 deceleration. The total time elapsed indicated how long the organ- 

 ism is occupied in reattaining balance. 



The times required for measurable restitution of basal rates of 

 exchange vary from 0.04 hour (Zoothamnium) to 70 hours (snake). 

 Nearly the whole range is present in one species (snake) when gain 

 is compared with loss. If the brevity of the time occupied in recov- 

 ery is any indication of a crucial state for survival, then water 

 deficit is the more ''dangerous" situation in all species tested. 

 But I have no evidence that death is actually avoided by the great 

 speed of the exchanges observed. 



Partial relations of the time for completion or half -completion 

 of recovery (fig. 101) to the body size and to peculiar body struc- 

 tures may be discerned. Thus, Arhacia egg finishes its adjust- 

 ments rapidly, Phascolosoma, a larger animal, slowly. The circu- 

 lation of body fluids is a correlative in transport of water, sup- 

 posedly enabling the 15,000-gram dog to eliminate through local 



