TONUS 545 



the new position lasts, indicate that they proceed from statolith organs, rather than 

 from the semicircular canals themselves. 



The change of tonus, as just remarked, is a permanent one, as long as the new 

 position of the head is maintained. 



In the experiments of Magnus and Wolf (1913), the preparation was so made that the 

 changes in length of the isolated triceps or vasto-crureus could be traced on smoked paper. 

 The above results were confirmed, and it was shown very clearly how, in this tonic state, a 

 muscle can have different lengths under the same load. 



Relation to Sympathetic Nerves. Certain facts have been brought forward 

 recently which appear to indicate that the tonic state of skeletal muscle may have 

 something to do with sympathetic innervation of this kind of muscle. But 

 caution must be exercised until further work. Boeke(1911) described accessory 

 nerve endings in various voluntary muscles, which appear to be of sympathetic 

 origin (see Fig. 175). In preparations A and C of Fig. 175, it will be seen that 

 there is continuity of the fibre going to the accessory ending with the plexus around 

 the small blood vessels. In a later paper (1913), Boeke shows that the accessory 

 endings do not degenerate on section of the motor nerves to the eye muscles, 

 whereas the motor endings do (see Fig. 175, B). De Boer (1913, 1) finds that the 

 normal tonus of the hind limbs of the frog and of the cat disappears when the 

 rami communicantes of the sympathetic ganglia are cut. 



If this be so, it seems that stimulation of the sympathetic should produce tonic contraction 

 of the muscles. In some experiments in which I stimulated the sympathetic of the frog for 

 another purpose, I did not observe any effect of this kind, but experiments should be made, 

 both on the frog and on the cat, for the special purpose. 



In a further paper, De Boer (1914, 2) finds that rigor mortis is more marked 

 on the normal side than on that in which the sympathetic rami have been cut. 

 This result suggests that the tonic state is associated with difficulty of removal of 

 the products of metabolism. The same investigator (1913, 2, and 1914, 1) brings 

 the prolonged contraction, caused by a single induction shock to a veratrinised 

 muscle, into connection with ' the normal tonic state. The electrical state 

 corresponding to this veratrine contraction is that of a prolonged steady negativity 

 of the longitudinal surface to the tendon, as if a continuation of the normal brief 

 state of negativity. De Boer thinks that the prolonged contraction is due to the 

 " sarcoplasm," as suggested by Bottazzi, and similar to that of smooth muscle. A 

 difficulty in this interpretation of the veratrine curve is that a stimulus to the 

 spinal cord, after section of the sympathetic rami, produces a prolonged contrac- 

 tion in a veratrinised frog. De Boer suggests that the accessory endings of 

 Boeke might be directly stimulated by the initial ordinary twitch. 



According to this view, normal tonus is also associated with a slow consumption of protein 

 material in the sarcoplasm under the influence of the sympathetic system. It is true that the 

 appearance of creatinine and uric acid in the urine, referred to above (page 289), would be 

 thus accounted for, but further evidence is required. 



It has recently been shown by Kure, Hiramatsu, and Naito (1914) that the 

 diaphragm is kept in a state of tonus by impulses from the sympathetic system, 

 conveyed by the splanchnic nerves. When these nerves are cut, the diaphragm is 

 drawn up into the chest by the negative pressure in the pleural cavity. 



Certain effects of adrenaline on skeletal muscle, which have been described, 

 are of interest in the present connection. As we shall see in Chapter XXII., this 

 product of the activity of the suprarenal glands has the special property of exciting 

 the nerve endings of the sympathetic system and producing the effect due to 

 stimulation of sympathetic nerves themselves. Has it then any effect on skeletal 

 muscle 1 ? Oliver and Schafer (1895, p. 263) found that the twitch of the voluntary 

 muscles in the frog and in the dog was considerably prolonged after an injection 

 of suprarenal extract, an effect similar to that of veratrine. But if the 

 sympathetic endings of Boeke were stimulated by the drug, one would expect that 

 a shortening of the muscle would take place without the application of a stimulus 

 to the nerve. Cannon and Nice (1913) have described experiments in which 

 injection of adrenaline enabled a muscle in situ in an animal to continue con- 

 tracting longer, without fatigue, than in the absence of the drug. This effect is 



