1890.] of the Rigidity of the Earth. 75 



and for glass (^ = 5) the value of e is about T53 as given by (6) 

 and about 154 as given by (c). To compare the heights of the 

 tides in these cases with those given by the ordinary equilibrium 

 theory we have to multiply by §, the result is the fraction by 

 which the height of the tide is reduced by the elastic solid yielding. 

 It is as in the case considered by Thomson and Tait about i when 

 the rigidity is that of steel, and about § when the rigidity is that of 

 glass. 



May 12, 1890. 



Mr J, W. Clark, President, in the Chair. 



The following communications were made : 



(1) The action of Nicotin upon the Fresh-iuater Crayfish. By 

 J. N. Langley, M.A., F.R.S., Trinity College. 



When 1 to 3 mgs. of nicotin, in a 1 p. c. solution, are injected 

 beneath the epidermis of a crayfish, there is a very remarkable 

 paralysis of certain functions of the nervous system. Almost 

 immediately after the injection there is a tetanic contraction of 

 the striated muscles of the body, so that the eye-stalks are drawn 

 in, the antennae and antennules bent backwards, the ambulatory 

 legs are flexed, the claws firmly closed, and the tail bent. This 

 tetanic condition lasts for a minute or two only. Before it passes 

 off, or a little after it has done so, there is a strong peristalsis of 

 the intestine with a rhythmic movement of the vent; the duration 

 of this is variable, it may go on for an hour or more ; for a time 

 after it has ceased the movement of the vent can be readily pro- 

 duced by local stimulation. But neither the tetanic contraction of 

 the striated muscles nor the rhythmic movement of the unstriated 

 muscles are effects peculiar to nicotin ; many other substances have 

 a similar action. 



After the tetanic period, there follows a period of complete 

 fiaccidity of all the striated muscles, the respiratory movements 

 have ceased, and there is no movement of any segment; reflex 

 movements are for a short time abolished, but soon slight sluggish 

 reflex movements of flexion or extension may be obtained from any 

 one of the ambulatory legs by scratching the shell of the leg; the 

 movement is usually local, though sometimes the segment above 

 and the segment below also move. 



In a quarter of an hour or more, — the time varying with the 

 amount of nicotin given and with the condition of the crayfish — 

 the normal movements of the scaphognathites begin again, about 

 the same time the flagella start their active, lashing movements, and, 

 though as a rule somewhat later, there are fairly normal rhythmic 

 movements of the swimmerets. Each of the three structures 



