PSYCHOLOGICAL MEASUREMENTS. 593 



varied from 2 to 45 mm. The standard deviation for the series was 

 11.4 mm., thus showing a coefficient of variability for the series of 

 76 per cent.^ The time interval separating the two stimuli to the 

 patellar tendon was gradually changed to determine that time separa- 

 tion when the second stimulus failed to produce a measurable reflex. 

 (See p. 157.) This interval (S) varied from 0.11 to 0.42 second. 

 In 39 cases in which the measurements were fairly satisfactory, the 

 average was 0.25 second.^ The standard deviation for our series of 

 39 S values is 0.076. The coefficient of variability for this refractory 

 period measure is found to be 30 per cent.^ 



We have mentioned the variability in the latency, amplitude, and 

 the refractory period of the patellar reflex for different subjects. We 

 might also call attention to a similar variability between successive 

 series of records on the same subject. Dodge and Benedict have called 

 attention to this factor and have given illustrative data on page 46 

 of their publication. It is known that in the case of the protective lid 

 reflex, if we use sharp noises as stimuli for the eye wink, the individual 

 gradually becomes accustomed to this stimulation and the wink is 

 inhibited, either showing a large decrease in its amplitude or being 

 absent altogether. The same series of changes occur in the case of the 

 patellar reflex. The reason for it is not so obvious as in the protective 

 lid reflex. Nevertheless the stimuli commonly become more or less 

 ineffective in that the amplitude of the reflex decreases if the measure- 

 ment is taken every few days. Something of the same phenomenon 

 shows in most series of reflexes taken at one sitting. The first few of 

 the set may be much larger than those which follow. This same 

 condition is of course true also with lid reflexes. 



In attempting to use the patellar reflex in this low-diet investigation 

 we recognize these elements of difficulty in making the measurements 

 uniform and in interpreting the data. However, in conformity with 

 our general purpose of providing as many opportunities as possible 

 for the unknown effect of a prolonged reduced diet to demonstrate 

 itself in the neuro-muscular processes, and since it was not convenient 

 to use other reflex measurements, we have employed it here. The 

 results are rather disappointing in the sense that the data (see tables 

 165 and 166) appear to be so fragmentary. Of the members of Squad 

 A the patellar reflex could never be secured from Pea; it was always 



^Dodge, Zeitschr. f. allg. Physiol., 1910, 12, p. 27. It would appear that Professor Dodge's 

 statement "I believe the amplitude of the response in the knee jerk should be used with extreme 

 caution as an indicator of the variations of any one selected factor; slight variations in the mean 

 should be viewed with especial distrust," is thoroughly justifiable. 



^Dodge and Benedict and later Miles worked with a separation of 0.5 second. The secondary 

 reflexes under these conditions were usually of considerably less amplitude than the primary 

 reflexes, but the reflex arc was never totally refractory with this separation between the stimuli. 



'It is rather unfortunate that in the form Dodge and Benedict (see Carnegie Inst. Wash. Pub. 

 No. 232, 1915, p. 49, ff.) published their data the values for latency and for reflex amplitude 

 were not given directly, but only the differences between successive series of such measurements; 

 comparisons can not therefore be made. 



