334 



PHYSIOLOGY 



other muscles, such as the tendo Achillis, the triceps, and the extensor 

 muscles of the wrist, but with not so great ease as is the case with the knee. 

 The knee-jerk is not altered by rendering the tendon anaesthetic by section 

 of all its nerves. The essential feature is a slight passive increase of the 

 trillion to which the muscle is already subjected. Mere tension of the 

 musele is not however the only factor. The tone which is reflexly 

 maintained in (lie muscle is necessary for this response to direct stimulation 

 to take place. The knee-jerk is therefore of special im 

 portance as an index to the tonic condition of the 

 muscles concerned, being brisk and easily elicited when 

 the tonus is pronounced, and slight or absent when the 

 tone of the muscle is depressed. 



The tone of the muscles, as well as the consequent 

 tendon phenomena, is dependent on the integrity of 

 the reflex arc governing the muscles in question. It 

 has been shown by Sherrington that the afferent part 

 of the arc is represented by the afferent nerves from the 

 muscle itself, and that these nerves receive their sense 

 impressions from the special nerve-endings characteristic 

 of muscle the ' muscle-spindles.' Even in the purely 

 muscular nerves a large proportion of the fibres are 

 afferent in function and, after section of the appro- 

 priate posterior roots distal to the ganglia, as many as 

 40 per cent, of the fibres going to a muscle may be 

 found degenerated. Though most of HUH- have the 

 muscle- spindles as their destination, a certain number 

 pass to the tendon and aponeuroses connected with the 

 muscle, where they end in the end-organs known as the 

 organs of Golgi and the organs of Ruffini. After 

 tion of the motor nerves the muscle fibres degenerate, 

 I.: 107. Hind part w ith the exception of the modified fibres which, enclosed 



of a spinal frog, . 



hung up by the in. a connected tissue sheath, are concerned in the lor ma 



jaw. The posterior ^ion o f the muscle-spindles. Muscle tone and tendon 

 i ")(8 of the nerves . 



to the left hind phenomena may therefore be abolished by lesions ot 



ii'nh have been afferent nerves, which leave a considerable part of 

 divided. 



(BECHTBREW.) the cutaneous sensibility of the limb intact. In man 



the spinal reflex mechanism connected with the knee 

 jerk is situated in the third and fourth lumbar segment.-. 'I he jerk may be 

 aboli>hed by sect ion of the third and fourth posterior nerve-roots, although 

 t render the \\holr hind limb anaesthetic it would be necessary to divide all 

 the roots from the second lumbar to the fourth sacral inclusive. 



The extremely short period which elapses between the moment of striking 

 the tendon and the contraction of the muscle, which was found by Gotch 

 to be only about '005 second, has been thought to prove that the tendon 

 reflex must be due to direct stimulation of the muscle and could not be 

 of the nature of a true reflex. It was therefore suggested that the func- 



