412 JOHN LINCK ULRICH 



right position during progression, in accordance with the existence 

 at the time of a reflex standing position or of progression, before 

 there occurred a modification of the position of the limbs and 

 body of the animal. Both modifications, that of a standing posi- 

 tion before the latch of the latch-box problem, and one of upright 

 progression to it, may occur in rats when standing, or when pro- 

 gression existed before posture was attained to produce the neck 

 reflex movement. Evidently, all movements are inherently co- 

 ordinated with progression, for rhythmic extension and flexion 

 of the rat's limbs are more fundamental than any other inte- 

 grated movements produced in the rat. 



Great variation exists in the functional condition of all reflex 

 thrusts of both fore and hind limbs. When their functional con- 

 dition is the best, passively moving the head slightly, or even 

 touching the snout or vibrissae will at once evoke strong exten- 

 sor thrusts. Opening the mouth or tickling the lips will produce 

 similar responses of the limbs, with shaking of the head. On 

 the other hand when these reflex thrusts are poorly developed, 

 they can sometimes be evoked on the first and succeeding tests, 

 the extensor tone gradually growing stronger with an increase 

 spread of excitations in the receptors of the neck and the laby- 

 rinth of the ear, or the extensor tone becomes weaker with each 

 test, or, the thrusts can be evoked on the first test and not there- 

 after. Sometimes the reflex thrusts cannot be evoked on the 

 first test, but only on the second, third or fourth test, and then 

 the extensor tones are usually weak. Those evoked on the second 

 test have usually a stronger extensor tone than those evoked on 

 the third or fourth. In some rats no reflex extensor thrusts can 

 be evoked after repeated tests. The individual differences are 

 very great in respect to the time of the appearance of these 

 reflex thrusts, and this seems to indicate an unequal antagonistic 

 action of extension and flexion of them or an undeveloped condi- 

 tion of them. This undeveloped condition must reside in the 

 centers for the production of these thrusts, for repeated tests do 

 not in all cases spread excitations in receptors to evoke them. 

 An increase in excitations happens only when repeated tests 

 increase the extensor tone of the limbs. 



