REFLEX ACTIONS. 153 



were shown to be much more independent of the direct control of 

 the central nervous system. While these organs in the experiments 

 under consideration were still in connection with the sympathetic 

 ganglia and in part with the brain through the vagi, still their 

 connections with the central nervous system, particularly as 

 regards their sensory paths and the innervation of the blood-vessels, 

 were in largest part destroyed. The immediate effect of this 

 destruction would have been the death of the animal if the care 

 of the observer had not replaced, in the beginning, the normal 

 control exercised by the nervous system through the spinal nerves; 

 but later this careful nursing was not required. While these organs, 

 therefore, are capable of a certain amount of independent activity 

 and co-ordination, they are normally controlled through the various 

 reflex activities of the brain and cord. In the third place, it is 

 noteworthy that the adaptability of the cordless portion of the 

 animal was distinctly less than normal. Its power of preserving a 

 constant body temperature was more limited than in the normal 

 animal, and the susceptibility to inflammatory disturbances in the 

 visceral organs was greatly increased. It seems evident, from these 

 facts, that, although the animal was hving, its power of adaptation to 

 marked changes in the external or internal environment was greatly 

 lessened, and this fact illustrates well the great general importance 

 of the spinal cord and brain as reflex centers controlling the nutri- 

 tion and co-ordinated activities of the body tissues and organs. 

 This control is necessary under normal conditions for the success- 

 ful combination of the activities of the various organs. A large 

 part of this control is doubtless dependent upon the regulation of 

 the blood supply to the various organs. The mechanism by which 

 this is effected and the parts played by the cord and the brain, 

 (medulla oblongata), respectively, will be described in the section 

 on Circulation. 



Knee-jerk.^ — Knee-jerk or knee-kick is the name commonly 

 given to the jerk of the foot when a light blow is struck upon the 

 patellar ligament just below the knee. The jerk of the foot is 

 due to a contraction of the quadriceps femoris muscle. Accord- 

 ing to Sherrington, the parts of this muscular mass chiefly 

 concerned are the m. vastus medialis and m. vastus intermedins. 

 In order to obtain the muscular response it is usually neces- 

 sary to put the quadriceps under some tension by flexion of the 

 leg. This end is achieved most readily by crossing the knees 

 or by allowing the leg to hang freely when sitting on the edge 

 of a bench or table. Under such circumstances the jerk is 

 obtained in the great majority of normal persons, and this 

 fact has made it an important diagnostic sign in many diseases 

 of the spinal cord. The importance of the reaction for such 



