GENERAL PHYSIOLOGY OF NERVE-TISSUE. 131 



veying the current to or from this part should be of a size sufficient 

 to localize the current and to increase its density. It was discovered 

 by Duchenne that there are certain points all over the body stimula- 

 tion of which is more quickly followed by muscle contraction than 

 others. It was subsequently discovered by Remak that these points 

 coincide with the entrance of the nerve into the muscle. It is to 

 these motor points that the one electrode should be applied. The 

 position of some of these points on the forearm is shown in Fig. 



57- 



Reactions of Degeneration. In consequence of the degen- 

 eration and changes in irritability which occur in nerves and muscles 

 when separated, either experimentally or as the result of disease, the 

 response of these structures to the induced and the make and break 

 of the constant current differs from that observed in the physiologic 

 condition. The facts observed under the application of these two 

 forms of electricity are of importance in the diagnosis and thera- 

 peutics of the precedent lesions^. The principal difference of behavior 

 is observed in the muscles, which exhibit diminished or abolished 

 excitability to the induced current^wh'ile at the same time manifesting * 

 an increased excitability to the constant current^gojnuch so -is this the f^ 

 case that a closing contraction is just as likely to occur at the positive 

 as at the negative pole^-This peculiarity of the muscle response is 

 termed the reaction of degeneration. The synchronous diminished 

 excitability of the nerves is the same for either current. The term 

 "partial reaction of degeneration" is used when there is a normal 

 reaction of the nerves, with the degenerative reaction of the muscles. 

 This condition is observed in progressive muscular atrophy. 



Reflex Action. Inasmuch as many of the muscle movements of 

 the body, as well as the formation and discharge of secretions from 

 glands, variations in the caliber of blood-vessels, inhibition and 

 acceleration in the activity of various organs, are the result of stimu- 

 lations of the terminal organs of afferent nerves, they are termed, for 

 convenience, reflex actions, and, as they take place for the most part 

 through the spinal cord and medulla oblongata and independently 

 of the brain or of volitional influences, they are also termed involun- 

 tary actions. As many of the processes to be described in succeeding 

 chapters arex)f this character, requiring for their performance the 

 cooperation of several organs and tissues associated through the 

 intermediation of the nervous system, it seems advisable to consider 

 briefly, in this connection, the parts involved in a reflex action, as 

 well as their mode of action. As shown in Fig. 58, the necessary 

 structures are as follows : 



1. A sentient surface, skin, mucous membrane, sense-organ, etc. 



2. An afferent nerve- fiber and cell. 



3. An emissive cell, from which arises 



