Royal Society. 295 



the preliminary processes of digestion are at an end, and thus also the 

 child grows and the uterus expands, and labour pains do not begin 

 until the growth of the child is completed, and the stimulus of that 

 growth suspended. 



(e.) That heat and cold do not stimulate contraction, because con- 

 traction does not happen until the natural polar action of the muscle is 

 suspended, — an event which happens equally under either extreme of 

 temperature, — and thus the muscle would seem to contract because 

 the heat or cold extinguishes that polar action of the muscle which 

 antagonizes contraction. 



(/.) That light cannot cause contraction, (1) because it exercises 

 a directly opposite influence upon the irritable cushions of the sensi- 

 tive plant; and (2) because it is as easy to agree with Bichat, and 

 suppose that light expands the curtain of the iris, as that it causes 

 contraction in sphincter-fibres surrounding the pupil, which fibres 

 have no existence. 



(g.) That chemical and mechanical agencies do not stimulate con- 

 traction, because contraction does not happen until the agent has de- 

 stroyed that polar action of the muscle which antagonizes contrac- 

 tion (Eckardt). 



It is argued, also, that the action of the will upon muscle is not 

 necessarily that of a stimulus, for the will may act by withdrawing 

 something from the muscle as well as by communicating something 

 to the muscle, and, if so, then the previous considerations enhance 

 the probability that it acts by withdrawing something. 



In the course of the argument it is further shown that this con- 

 clusion is borne out by the history of the muscular movements which 

 are manifested in the coats of vessels and in the heart, while at the 

 same time this view is found to give the clue to the physical inter- 

 pretation of " capillary action," and of rhythm, whether this be in 

 the heart or elsewhere. 



It is shown, also, that the same conclusion is borne out by the 

 pathology of tremor, convulsion, and spasm, — of those diseases, that 

 is to say, in which muscular contraction is in excess. Thus, (to 

 mention one argument out of many,) the state of circulation which 

 is invariably associated with tremor, convulsion, and spasm, is one 

 which necessarily implies the diminution of all accustomed stimu- 

 lation in the muscle, for it is a state which borders closely upon 

 syncope or asphyxia. 



And, lastly, it is shown that there is nothing in the phasnomenon 

 of muscular contraction which need prevent it from being referred to 

 the operation of that common principle of attraction which belongs 

 to muscle in common with all matter, and thus the general conclusion 

 is that another barrier between the organic and inorganic world is 

 broken down, and that muscular contraction is an effect of the 

 universal law of gravitation. 



There are, however, sundry grave objections to this theory, and 

 MM main object of the paper under consideration is to remove them. 

 Thu>, for example, if muscle contracts when nervous influence is 

 withdrawn, how is it that it relaxes when the nerve is divided or 



