232 PHYSIOLOGICAL EEGULATIONS 



rates of urea clearance may bear a different relation during rising 

 water loads than during falling loads. Further, at one load the 

 urinary rates are often higher following sudden accession of water 

 to the body (§12) than during decrease of load. 



Rates of excretion of urea (Marshall, '20) and chloride (Kings- 

 ley) suddenly augment, when the rate of water excretion augments 

 following ingestion of water. Chloride is eliminated four times as 

 fast as without water ingestion, then its output subsides before 

 water excretion diminishes ; as though the sudden increase of water 

 excretion caught the processes of solute excretion napping, and 

 some time were required to exact the separation of each solute from 

 the flood of water. The ratio of solute output to water output is 

 accordingly found to be smaller in proportion as more of each has 

 been just previously excreted. 



In brief, while the content and elimination of urea and other 

 substances are being influenced by water content and exchange, the 

 concentrations of many or all substances in blood and other tissues 

 are simultaneously affected. Evidently (1) the changes of concen- 

 tration noted in section 79 are not solely those of dilution; (2) time 

 factors loom larger than load factors in some of them; (5) other 

 methods than those measuring rate of urea excretion alone are 

 required to ascertain whether the production of urea is affected by 

 water content ; similarly for any other component. 



(5) Neuromuscular activities have been noted only in qualita- 

 tive fashion. In extreme positive loads of water the dogs of Rown- 

 tree ('23) exhibited muscular twitchings, hyperirritability, as- 

 thenia, ataxia, vomiting, coma, convulsions, and death. Each is a 

 type of behavior capable of quantitative study at known water 

 loads ; several may hasten the recovery of the animal toward water 

 balance. Individual reflexes and responses are equally susceptible 

 of evaluation, and might be found modified at moderate water 

 loads. 



In extreme negative loads, still fewer observations are recorded. 

 Anorexia, vomiting of food, restlessness, ataxia, and death are 

 known. Dyspnea is prominent (Pernice and Scagliosi, 1895) but 

 panting in response to concomitant heat is slower to start (Greger- 

 sen, '31 ; Dontas, '39 ) . All instances in which ' ' thirst drives ' ' have 

 been induced in dogs may furnish material for the present study. 

 "Water load, in turn, is a proper measure of the intensity of these 

 urges or drives to activity. 



