20 
Proceedings of the Eoyal Society of Edinburgh. [Sess. 
(The total salts present in the fluid, half an hour after immersion, varied 
from 006-009 grm. ; these were taken to represent the residue of external 
salts after washing, and have been deducted from the “ total ” results given.) 
The above shows that a definite percentage of chlorides is invariably 
lost, whatever the age of the animal, though the total chlorides necessarily 
depend on the gross weight. This plainly indicates the cause of death — 
diminished tonicity of the body fluid, due both to loss of salts and to oedema, 
or rather hydraemia. Hence, the period of survival will depend on the 
rate of diffusion of salts out of the crabs and on the onset of oedema, thus 
reducing the question to one of permeability of the membranes of the 
animal. Similar conclusions have also been reached by Plateau (10), by 
Loeb (6) working on Gammarus, and by Abbott (1) on the Fiddler crab. 
Loeb has not only shown that death is due to loss of salts, but that the 
onset of death depends on the disturbance of the antagonism between the 
sodium, potassium, and calcium ions of the animal’s fluid. With the excep- 
tion of Plateau, however, the question of moult has not been dealt with. 
Smith (12) and Paul and Sharpe (9) have pointed out that the changes 
occurring during moult involve, not only the integuments, but also the 
general metabolism ; and since it has been shown that the moult cycle 
profoundly modifies the duration of survival, the condition of the blood as 
well as that of the membranes is of obvious importance in considering the 
rate of loss of salts. 
With regard to the blood, Cuenot (4) states that preparatory to moult 
a crab imbibes a considerable amount of fluid through its alimentary canal. 
Further information is supplied by Paul and Sharpe (9), who have shown 
that although the volume of the blood is increased, the calcium percentage 
remains unaltered ; whether this holds true for sodium and potassium is 
not mentioned. This result, however, indicates that the total calcium has 
been increased ; and if the total sodium and potassium were not similarly 
increased, according to Loeb the equilibrium would be disturbed, with 
resultant harm to the animal. Therefore it may be presumed, either that 
the three ions have been increased in due proportion, or that the excess of 
calcium in the blood is not in a dissociable condition (viz. calcium soaps — 
see Paul and Sharpe’s paper). If the latter presumption be correct, the 
blood would be in less concentration than normal ; whatever be the 
explanation, it is evident that under such conditions the animal suffers no 
ill effects. 
The other factor affecting permeability is the condition of the membranes. 
The present experiments uphold Plateau’s observations that the soft 
membranes of the newly moulted crab are extremely permeable. Histo- 
