418 JOHN LINCK ULRICH 



neck reflex is produced. Not one fundamental reflex movement 

 is difficult to perform. Posture is not excessive; that is, a large 

 number of muscles of the body do not contract to produce it, 

 and the neck reflex movement is very readily produced. Rapid 

 adjustment to the environment of every part of the problem 

 takes place, and the movements made, seem effective for every 

 part of the latch-box problem. The cumulative effect of all move- 

 ments performed soon establishes interaction of body parts 

 for the production of the neck reflex. 



This account holds good when the reflex mechanisms of the 

 rat are functionally developed, but if timidity is manifest, the 

 problem is not solved until this manifestation disappears, and 

 should timidity persist, the problem remains unsolved. Some- 

 tunes all the reflex thrusts may be evoked on the first trial and 

 for a few succeeding trials they appear functionally well devel- 

 oped, and then fluctuate Solution of the problem, then may not 

 occur so soon on the first day or not until a day or so later, at 

 times not until the reflex thrusts have again fluctuated. Evi- 

 dently in such cases, instability of the reflex thrusts or the pos- 

 sibility of instability in the future determines or prolongs the 

 tune when the problem will be solved. 



This last statement would also apply to rats in which the reflex 

 thrusts on the first trial are undeveloped. But here conditions 

 exist, depending upon whether reflex excitability is hypernor- 

 mal, or hyponormal. When reflex excitability is hypernormal 

 and the reflex extensor thrusts are functionally undeveloped or 

 asymmetrically so, then solution of the problem comes very soon, 

 sometimes as soon as when the reflex mechanism of the thrusts 

 is fully developed. Active movements result in posturing and 

 the production of the neck reflex; but posture is usually excessive 

 and a large number of muscles are used for its production. The 

 latch is raised by the neck reflex with great force and suddenness. 

 When reflex excitability is hyponormal, the solution of the prob- 

 lem does not take place usually on the first day, but may occur 

 on any one of the suceeding 5 days. The mechanism for the 

 production of reflex excitability must either be developed, or an 

 interaction of the body parts of the animal is slower in appearing 



