§ 5.221 PROTEIN METABOLISM 201 



This hormone may be the same as the moult-inhibiting hormone. 



Increased loss of proteins following eyestalk removal is also 

 claimed for Carcinus from measurement of nitrogen excretion. 

 This is partly due to the stress of wounding, since a similar effect, 

 but of only half the magnitude, results from leg amputation 

 (Needham, 1955). As no hormone injections were used to counter- 

 act this eifect, the evidence is not conclusive ; but it again suggests 

 that in non-moulting crabs an eyestalk hormone restrains protein 

 breakdown. 



During moulting the situation is different. Although the protein 

 content of the plasma is unusually high because of resorption from 

 the old skin, nitrogen excretion is particularly low. Needham 

 (1957) concluded that ''within limits the animal is able to control 

 its nitrogen output, whatever the external conditions". As moulting 

 proceeds most of the protein from the plasma is presumably 

 deflected into certain anabolic processes, such as the formation of 

 the new integument. These protein transfers would not of them- 

 selves alter the total proteins in the body. Nor does starvation 

 affect the issue, since most crabs do not feed for some days before, 

 during or after moulting. 



Koch (1952) confirms the view that the nitrogen and protein 

 content of the body remains remarkably constant during moulting, 

 and is not affected by the absence of any eyestalk hormone. 

 Incidentally, the moult-inhibiting hormone is not released from 

 the eyestalk at this stage (Part II, § 3). Koch examined the nitrogen 

 content of the mitten crab, Eriocheir sinensis, and found that the 

 eyestalks have no effect upon the nitrogen metabolism, at least 

 during the first experimentally induced moult. There is no 

 difference in the ratio of nitrogen content to size, in the cast skins 

 of crabs moulting normally and those induced to do so by eyestalk 

 removal. The ratio of total nitrogen content to carapace width 

 measured before moulting is the same, within limits, for moulting 

 and non-moulting control crabs, and for operated crabs (between 

 curves. Fig. 5-11). After an induced mouh, the ratio of nitrogen 

 in body and cast skin to carapace width, measured after moultmg 

 in the operated crabs, is significantly lower (B, Fig. 5-11) than 

 before, by an amount that seems to be proportional to the increase 

 in water content that follows from the absence of the diuretic 



