326 



PHYSIOLOGY 



CHAP. 



which was deduced by us as early as 1879 from the critical analysis 

 of periodic respiration (Vol. I. p. 492). 



Langendorff (1905) has recently confirmed Fano's observations 

 for the oscillations of intensity in the reflex movements of the 

 tortoise. But he was unable to admit their dependence on 

 impulses from the bulb, since they persisted after high tran- 

 section of the cord. Scheven in the rabbit noticed analogous 

 oscillations of the patellar reflex, which is evoked by the rhythmical 

 application of single mechanical stimuli (infra). 



According to G. Cesana (1911), in the new-born rat oscillations 

 in the height of the reflex contractions are seen from the earliest 



FIG. 188. Knee-jerk. A, the dotted line indicates the movement produced by tapping the 

 patellar tendon ; B, the same obtained by a hammer when it does not occur readily in the 

 usual way. 



days of life, and these, contrary to what occurs in the adult, persist 

 even after transection below the medulla oblongata. 



The phenomenon of " knee-jerk" first studied by Westphal and 

 by Erb, is strictly related to the tone of the skeletal muscles. 



When the limb is hanging with all the muscles at rest a light 

 blow on the patellar ligament with the hand, or better with a 

 small hammer, evokes a sharp contraction of the quadriceps cruris 

 and an extension of the knee (Fig. 188). Similar effects are seen 

 in other muscles on mechanically exciting the muscles and tendons 

 or the periosteum, but the knee-jerk is the most typical and the 

 best studied. 



The indispensable condition for the appearance of the knee-jerk 

 is some tension or tone in the muscle. The stimulus which evokes 

 the reaction consists in a gentle but sudden passive increase of 

 this tension. 



