CAUSE OF MUSCULAR CONTRACTILITY. 143 



organisms, in which no nerve-tissue has been shown to exist. Con- 

 tractile tissues are met with even in certain plants, though these are 

 believed to be absolutely destitute of a nervous system. Muscular 

 contractions, it is alleged, will occur in the muscles of the embryos of 

 animals, even whilst none can yet be excited by stimuli applied to the 

 nerves. Subsequently to the division of its nerves, a muscle, provided 

 that its nutrition is maintained, retains or recovers its power of con- 

 tracting on the direct application of a stimulus, long after it ceases to 

 act on the stimulation of the divided nerve. Chloroform and ether 

 suspend the power of the nervous system over the muscles, so that 

 stimuli applied to the nerves no longer excite muscular contraction, 

 although the contractility of the muscle itself, as shown by direct 

 stimulation of its fibres, yet remains, and although the effects on the 

 sensory nerves lead us to infer that these reagents act quite up to the 

 extremities of the motor nerves also. There exists, moreover, a special 

 poison, the woorari or curare, which is said to have the power of de- 

 stroying the vital properties of conductility of the nerves down to 

 their finest extremities, and yet permits the muscles to retain their 

 contractility on the application of a direct stimulus. Lastly, in the 

 case of a muscle like the sartorius muscle of the frog, which is pro- 

 vided with a nerve distributed to its central part only, the muscle can 

 be made to contract at its extremities, after the destruction of the 

 nerve itself (Kuhne). 



The preceding facts certainly tend to show that the muscular irrita- 

 bility is inherent in the muscle, and independent of the nerve. But a 

 further question arises, viz., whether, granting that the muscular 

 irritability is a property inherent in muscle, is it ever excited, or is it 

 capable of being excited directly, or can it only be so, through irrita- 

 tion applied indirectly to it through the nerves ? The minute distri- 

 bution of the finest non-medullated extremities of the nerves among 

 the muscular fibres, and their intimate connection with them, render 

 it impossible to separate the effect of a stimulus upon the one and the 

 other, so as to be able to say that a stimulus has acted on the muscle 

 only, and not also on the fine branches of nerves mixed up with, or 

 distributed upon, its fibres. The two last-mentioned experiments, viz., 

 that on the effects of the woorari poison, and that on the sartorius 

 muscle of the frog, are maintained by some to have solved this ques- 

 tion, and to have shown that the inherent power in muscle is capable 

 of being directly excited, i. e., idio-motorially, without the intervention 

 of even the minutest extremities of the nerve-fibres, as well as neuro- 

 motorialty, or through the agency of the motor nerves. 



As to the ultimate cause of muscular contraction, it is quite evident 

 that the slight condensation, if any, which takes place in the tissue 

 during contraction, is wholly insufficient to account for the latter 

 phenomenon. It is certain only that the tendency of the sarcous 

 elements or disdiaclasts to alter their shape by shortening or widen- 

 ing themselves, and so to approach each other in a definite direction, 

 is the essential fact in this remarkable phenomenon. Why they ap- 

 proach each other, is not yet explained. It has always been assumed 

 that the state of contraction is the active, and the state of relaxation 



