188 



and being re-established, the muscle relaxes (just as it does in 

 the case where paralysis is caused by division of the nerve), and 

 tremor, convulsion and spasm are at an end. Nor is there any doubt 

 that the nerves are paralysed when the circulation fails to the point 

 which is here supposed. Thus, if the circulation in the hand be 

 depressed by immersion in cold water, the sense of touch and the 

 power of movement are partially or wholly destroyed ; or if the 

 principal vessel of a limb be tied, the nerves are similarly paralysed 

 until the collateral circulation be established ; and in each case, also, 

 the power of provoking " reflex movements " is diminished or de- 

 stroyed. In either case the nerves are more or less paralysed for 

 want of blood, and, if so, it surely follows that the nerves must be 

 paralysed, and still more effectually, when the circulation fails as it 

 fails in syncope, asphyxia, or death, and when the movement of the 

 blood is almost or altogether at an end. Hence it is quite intelli- 

 gible that tremor, convulsion or spasm should be caused by want of 

 blood, as is stated in the argument, and that they should cease in 

 syncope, asphyxia, and death ; and thus this objection falls to the 

 ground, and with it all objections of the same kind. 



Such is an imperfect sketch of the evidence upon which the phy- 

 sical theory of muscular contraction is founded. 



II. " On the Structure of some Limestone Nodules enclosed in 

 Seams of Bituminous Coal, with a Description of some 

 Trigonocarpons contained in them." By J. D. HOOKER, 

 M.D., F.R..S., and E. BINNEY, Esq. Received November 

 23, 1854. 



The authors first describe the occurrence of the limestone nodules, 

 which form a continuous bed in the centre of a thin seam of bitumi- 

 nous coal in the lower part of the Lancashire coal-field. The no- 

 dules were of various sizes, some weighing many pounds, and caused 

 the coal to bulge out both above and below them, and they were 

 found to be entirely composed of vegetable tissues converted into 

 carbonate of lime and magnesia. Their formation is supposed by 

 the authors to be due to infiltration of water through the superin- 



