Chapter XXI 

 CONCLUSIONS 



§ 174. Physiological regulations have now been described in 

 quantitative terms, thereby gaining a foundation in facts and rela- 

 tions. Regulations are simply those relations according to which 

 the properties of organisms persist. The organisms that were 

 studied seem to have themselves argued the manner in which they 

 are kept constant. I will try here to recount the general features 

 that have turned up among the specific details already provided. 



§ 175. Abstract of the investigation 



I wanted to study how a given property or content of an organ- 

 ism is preserved during life. How constant the content is, could be 

 ascertained by observing what successive numerical values it has, 

 and ultimately expressing those values by some statistic of scatter. 

 What happens to restore it after it has been disturbed from its 

 usual value, could be found by measuring the rates of its change or 

 exchange, especially during recovery. How the organism fore- 

 stalls the occurrence of disturbances, could be learned by seeing 

 how often the organism frequents an environment that either mini- 

 mizes or promotes exchanges, instead of some other environment. 



I first tried to find how the content of water in the whole body 

 of the dog is maintained. How long does recovery from a higher 

 or a lower amount than usual take? I measured not only content 

 and its change in relation to time, but also all exchanges of water 

 (gains and losses) in relation to increments (loads) in content of 

 water. It turned out that gain and loss are equal at only one con- 

 tent (balance). In all excesses losses are faster than gains, in all 

 deficits gains are faster than losses ; thereby balance is recovered. 

 Variability of water content I ascertained by weighing the dog at 

 successive equal intervals of time. Content is corrected periodi- 

 cally by the dog's ingestion of water, and more gradually by the 

 dog's excretion of urine (§25). 



Then I looked at other species. Man, frog, rat, rabbit, earth- 

 worm, and ameba, each use some particular rate and kind of water 

 transfer to compensate for water loads (equilibration). Several 

 that were tested, notably the rat, showed preference for moist 



471 



