TONUS 543 



in the temperature of the preparation. In any case, it seems fairly certain that much less 

 metabolism is associated with the tonic form of contraction. This result again is to be com- 

 pared with the experiments of Parnas and of Bethe given above. 



The reader may also be reminded of the inefficiency of the sartorius muscle of 

 the frog when maintaining a weight by stimulation of its nerve 'with induction 

 shocks. This result led A. V. Hill (1913, 4, p. 319) to suppose that there must 

 be a more efficient mechanism for the purpose in the normal organism. It is 

 suggestive that Hill found, in the same series of experiments (p. 317), that the 

 amount of heat produced per unit of tension developed, is independent of the 

 frequency of the stimuli, provided that the latter are sufficiently rapid to cause 

 complete fusion of twitches. 



Pembrey (1903) noticed that the panniculus carnosus of the hedgehog, which 

 keeps the animal rolled up into a ball, was in a state of tonic contraction during 

 hibernation, a fact which adds confirmatory evidence to the view of Roaf that 

 decerebrate rigidity is not associated with any considerable increase in metabolism. 



Heat Production. I have myself made some experiments (1912, 3) on the heat production 

 in muscles in decerebrate rigidity. Although the work is not yet complete, I found that there 

 is a certain amount of heat produced, in magnitude varying with the degree of tonic contrac- 

 tion, although it is undoubtedly very much less than that produced in an artificial tetanus of 

 a similar height. 



Electrical Change. According to Buytendyk (1912), the electrical change in decerebrate 

 rigidity, as shown by the string galvanometer, is discontinuous ; a fact which leads him to 

 regard it as a periodic discharge fronr nerve centres, similar to tetanus. Hofmann (1913) finds 

 a similar oscillatory discharge in the normal tonus of the eye muscles of the rabbit. We are 

 not compelled, however, to consider this to be the same thing as ordinary tetanus ; the 

 putting in action or removal of the "catch" mechanism might take place in a series of dis- 

 charges. Sherrington's inhibition experiments show that the relaxation is not instantaneous. 

 The amplitude of the electrical waves is less than in ordinary reflex tetanus. But it is not 

 possible to lay much stress on this fact, since it might be caused by the phases of contraction 

 not being synchronous in all fibres. Buytendyk, however, points out that the oscillations in 

 his curves are very regular, which seems to indicate synchronous state of contraction in all 

 fibres. 



Production of Creatine. Pekelharing and van Hoogenhuyze (1910) found an- 

 excess of creatine in invertebrate muscle in tonus, and Pekelharing (1911) found 

 creatinine in the urine of men after prolonged voluntary tonic contraction, but 

 not after walking. The results of Cathcart and Leathes on uric acid have been 

 mentioned previously (page 289). Leathes and Orr (1912), further, repeated 

 Pekelharing's experiment and found both uric acid and creatinine increased. 



Relation to Labyrinth. Ewald (1894) pointed out the important relation of 

 the labyrinth to the maintenance of tone in the muscles generally and the loss 

 of tone resulting from destruction of the semicircular canals. More detailed 

 investigations were made by Magnus and De Kleijn (1912) by the use of a 

 method devised by the latter. It was found that the tonic contraction of the 

 limb muscles in decerebrate rigidity, especially those of the fore limbs, -was greatly 

 influenced by changing the position of the head. Further analysis showed that 

 there are two factors at work, reflexes from receptors in the labyrinth and reflexes 

 from proprio-ceptors of the muscles of the neck. The former are concerned with 

 the relation of the head to space, independently of its relation to the trunk. The 

 latter are concerned merely with the position of the head in relation to the 

 trunk. The labyrinth can be rendered inoperative by the injection into it of 

 a 20 per cent, solution of cocaine, according to the method of Do Kleijn (1912). 

 The neck effect can be excluded by making the neck immobile on the body by 

 encasing it in plaster of Paris. It was found that the labyrinth receptors are 

 not affected, as regards their influence on tonus, by change of position in a 

 horizontal plane, but changes in the vertical plane have great effect on the tonus 

 of the limbs. When the head is in such a position that the vertex is upwards and 

 the nose at an angle of about 4o looking downwards, extensor tonus is minimal ; 

 with the vertex downwards, and the nose at 45 upwards, that is, on rotation 

 of 180, tonus is maximal. It was noticed that, along with contraction of the 

 extensors, there was inhibition of the flexors. Moreover, in this connection it 

 is interesting to note that Magnus and Wolf (1913) subsequently found that 



