240 METABOLIC HORMONES 



evidence, referred to above, showing the importance of cortical 

 hormones in causing water diuresis. 



5.4 Balance of calcium and phosphates 



UnHke water and the monovalent electrolytes, calcium and 

 phosphates are of more importance in growth than in the direct 

 relation of the animal to its environment. The changes in their 

 concentration in the blood are, therefore, slower and less spectacu- 

 lar, and fewer observations seem to have been made upon them. 



Arthropoda. Despite the differences in the metabolic signifi- 

 cance of the control of calcium and phosphates, as compared with 

 the salts previously considered, the hormones concerned in their 

 control seem, nevertheless, to be derived from the same organs, 

 namely the Y-organ and eyestalk in the Crustacea (p. 222) but 

 not in the Insecta. In both classes, the changes in calcium and 

 phosphates are associated with moulting, since in these forms with 

 hard exoskeletons it is necessary for one or both salts to be with- 

 drawn from the old skin before it is shed. During this phase they 

 appear in the blood and rise to a maximum at the time of the moult, 

 and then decrease suddenly as they are re-incorporated into the 

 new shell, together maybe with fresh calcium rapidly absorbed from 

 outside sources. The changes are more marked in Crustacea, which 

 have heavily calcified shells, than in Insecta, where such structures 

 are unknown and would clearly be too heavy to permit flight in air. 



Vertebrata. Since vertebrate growth is a continuous process 

 and not as a rule accompanied by moulting, the changes in calcium 

 and phosphates are more gradual ; but the accumulation of these 

 salts is an essential preparation for their deposition in bone in the 

 later stages of growth. 



For convenience in recording what evidence has so far been put 

 forward on the action of hormones on these salts, their concentra- 

 tion in the blood will be used as the indicator. 



5.41 balance OF calcium 



5.411 Increase of calcium in the blood 



Crustacea. In Carcinus, a single injection of an extract of the 

 Y-ORGAN, that contains the moult-promoting hormone, MPH, 



