404 



PRINCIPLES OF GENERAL PHYSIOLOGY 



constrictor, or diminished by those called vaso-dilator. Fig. 110 shows the fact in 

 the case of the tongue. Stimulation of the sympathetic nerve causes contraction 

 of the small arteries and therefore decrease of the volume of blood in the organ ; 

 that of the lingual nerve, which contains the vaso dilator fibres, causes increase of 

 volume. We have already met with another instance in the salivary glands. 



The muscle called " retractor pen is," present in certain animals, is a strip of 

 smooth muscle arising from the anterior caudal vertebrae and inserted into the 

 glans penis. It forms a very convenient object for the investigation of the 

 properties of smooth muscle. Fig. Ill is a tracing obtained in some work 

 (hitherto unpublished) in which Starling and myself were engaged. It is .seen that 

 the initial state of the muscle is one of moderate tonic contraction, since it can be 

 relaxed by the stimulation of the pelvic autonomic nerves, and it can also be 

 increased by stimulation of fibres contained in the pudic nerves. 



Another instructive case is that of the \a,rge. pincers of the Crayfish. There is 



FlO. 112. IXXERVATION OF THE CLAW MUSCLES OF THE CRAYFISH, ACCOKDIXli TO TIIK WORK 



OF RICHET, BIEDERMAXX, MANGOLD, ETC. The two kinds of nerve fibres divide simul- 

 taneously and the terminal fibrils are distributed, one or more of each kind, to the same 

 muscle fibre, passing inside the sarcolemma to end in the muscle substance. 



here a powerful muscle closing the forceps, and a similar one opening it (see the 

 figure in Huxley's book, 1880, p. 93). It is clear that, if the strong closing 

 muscle remained in a state of contraction, the weaker opening muscle would be 

 powerless. Accordingly, it is found that, if the nerve trunk supplying the 

 appendage be excited in such a way that the forceps is caused to open, the closing 

 muscle is inhibited, along with the contraction of the opening muscle, and, when 

 the forceps closes, an opposite effect on the two muscles takes place. Richet 

 (1882) showed that a weak direct stimulation of the claw caused opening, and a 

 strong one caused closing, while Biedermann (1887, 1) showed that a weak 

 stimulation of the nerve caused a contraction of the opening muscle, coincidently 

 with inhibition of tone in the closing muscle, and that a strong stimulation had the 

 opposite effect on both. The explanation of these facts seems to lie either in the 

 existence of four sets of fibres in the nerve trunk, exciting for the closing muscle, 

 inhibiting for the opening muscle, exciting for the latter, and inhibiting for the 

 former ; or two sets of fibres, each of which divides into two branches, one branch 

 inhibiting the one muscle, while the other branch excites the antagonist muscle. 

 The fibres causing contraction of the closing muscle and inhibition of the opening 



