76 Mr J. N. Langley, The action of Nicotin [May 12, 



mentioned has at irregular intervals periods of rest, these are most 

 frequent and longest in the case of the swimmerets ; least frequent 

 and shortest in the case of the scaphognathites. The movements 

 can be stopped for a few seconds by various slight sensory stimuli. 



Although the scaphognathites, fiagella, and swimmerets thus 

 rapidly recover their ordinary rhythmic action, the crayfish lies as 

 it is placed and there is an almost complete absence of other 

 movement; there may be a slight slow movement of an ambulatory 

 leg, but this is probably of a reflex nature. This condition is, in 

 its chief features, maintained for one to two months. During this 

 time there is a progressive slight improvement in the reflexes so 

 that stimulation of any one segment causes a greater local effect 

 and gives rise more readily to movements in other segments. The 

 reflex movement however never becomes very active. The last seg- 

 mental reflex to recover is the closure of the great chelae on touch- 

 ing their inner surfaces ; there are some other odd points in the 

 order and extent of the recovery of the reflexes, but as these have 

 not been quite the same in all cases, I shall consider them at 

 a later time. If food is pushed into the oesophagus, it is apparently 

 carried on and digested, but I have not seen any recovery in the 

 power of the maxillae or mandibles to aid in taking up food; in one 

 case only (five to six weeks after nicotin injection) did the chelae 

 of the first two ambulatory legs close on placing a small piece of 

 food between them, but even then no movement was made to carry 

 the food to the mouth. 



Two months is the longest time for which I have kept a cray- 

 fish after it has received 2 or 3 mgs. of nicotin ; in every case there 

 was some cause, such as the cessation of the water supply, to which 

 death may have been due. I am, then, unable to say whether or 

 not the above-mentioned amount of nicotin is eventually fatal. In 

 the paralysed state of the crayfish, fungus rapidly grows on the 

 animal, and this unless frequently removed is sufficient to cause 

 death. 



The paralysing action of nicotin upon the crayfish is due to its 

 affecting the central nervous system, and not to its affecting either 

 the peripheral nerves, the nerve-endings, or the muscles. This can 

 be shown readily by giving nicotin to a crayfish and then stimu- 

 lating one of the peripheral nerves, the stimulation causes contrac- 

 tion in the muscles of that segment. 



It is clear also that the action of nicotin on the central nervous 

 system is to an extraordinary degree selective, that is to say, that 

 certain parts of the central nervous system are affected very much 

 more than others; thus the nervous action causing rhythmic move- 

 ments of the scaphognathites, fiagella and swimmerets soon 

 returns to its normal condition, whilst the nervous action lead- 

 ing to walking, swimming, masticatory movements, etc. are stopped 



