REFLEX ACTIONS. 149 



may give an augmentation or reinforcement of the reflex. A 

 striking example of this augmenting effect is given below in the 

 paragraph upon the knee-kick. 



Influence of the Condition of the Cord on its Reflex Ac- 

 tivities. The time and extent of the reflex responses may be 

 altered greatly by various influences, particularly by the action 

 of drugs. The effect in such cases is usually upon the nerve centers, 

 that is, upon the cells themselves or upon the synapses, that is to 

 say, the connections between the terminal arborization and the 

 dendrites the process of conduction within the sensory and 

 motor fibers being less easily affected. A convenient method 

 of studying such influences is that employed by Tiirck. In 

 this method the reflex frog is suspended, and the tip of the 

 longest toe is immersed to a definite point in a solution of sul- 

 phuric acid of a strength of 0.1 to 0.2 per cent. If the time 

 between the immersion and the reflex withdrawal of the foot is 

 noted by a metronome, or by a record upon a kymograph, it will 

 be found to be quite constant, provided the conditions are kept 

 uniform. If the average time for this reflex is obtained from a 

 series of observations it is possible to inject various substances 

 such as strychnin, chloroform, potassium bromid, quinin, etc. 

 under the skin, and after absorption has taken place to determine 

 the effect by a new series of observations. So far as drugs are 

 concerned the results of such experiments belong rather to pharma- 

 cology than to physiology. The method in some cases brings out an 

 interesting difference in the effects of various kinds of stimulation. 

 Strychnin, for instance, as was stated above, increases greatly the 

 delicacy of the reaction to pressure stimulation. At one stage in 

 its action before the convulsive responses are obtained the threshold 

 stimulus is greatly lowered, mere contact with the toes causes a 

 rapid retraction of the leg; whereas in the normal reflex frog a 

 relatively large pressure is necessary to obtain a similar response. 

 At this stage in the action of the strychnin the effect of the acid 

 stimulus, on the contrary, may be markedly weakened so far as 

 the time element is concerned. If the action of the strychnin is 

 not too rapid, it is usually possible to find a point at which the 

 time for the reflex is diminished, but this effect quickly disappears 

 and the period between stimulus and response becomes markedly 

 lengthened at a time when the slightest mechanical stimulation gives 

 a rapid reflex movement. This paradoxical result may depend pos- 

 sibly upon the variety of nerve fiber stimulated by the two kinds 

 of stimuli or may be connected with the fact that the acid 

 stimuli may bring about inhibitory as well as excitatory processes 

 in the cord. 



Reflexes from Other Parts of the Nervous System. Nu- 

 merous typical reflexes are known to occur in the brain. The 



