1^.6 



ni)Q cord i.s ui^;nel•. 



The tpbles of cornparHtive Buraaarieo of inclined plane 

 results support the hypothesip that the cieteriorution of Dr.-iin 

 weight in a strain of rats is accompHnif^fl by deterioration 

 in the ability to form hyt)it?. 



In Plate VIII is sliown the curve of learnint;; (belov/) 

 and of relearninti (above) of the inbred rats conpared v/ith 

 those of the normal control. The inbred curve is shown by the 

 solid line, that of the control oy the broken line. The ordi- 

 nates ^.ive the averaj^e time in seconds, and the abscissae the 

 number of the day in which such time was made. As in the other 

 learnin(_ curves, the average time for the first four days is 

 given in fit:ures. The descent for the fii-at ten days is quite 

 rapid, with one or two lapses. From the forty-first day the 

 normal curve lies entirely below the fo\ir second mark. The 

 inbred curve, throut^hout, shows great irregularities, especial- 

 ly on the thirtieth day when it rises to an averat^e of near- 

 ly twenty-eight seconds. The inbred curve of relearnint is 

 very similar to that of the normal, and from the twenty- third 

 day coincides with it. But it must be remembered that only 

 the best of the inbreds were used in the relearnin^i experiment; 

 eleven had failed to learn as at;^ain8t only two of the normals. 

 The inbreds used had all rpl earned at tne end of the twenty- 

 fourth day ; the normals at the end of the seventeenth day. 



In Plate IX may be seen the distribution curves of 

 learning of both the inbred and control series for the inclin- 

 ed plane experiment. The time is ^i^en in days — in tiroups 

 of five for learnin^i, eint^ly for relearnin^i. As is the case 

 with the mar.e experiment, it is very apparent that the advan- 

 tate lies wholly in favor of the normal control series. 



Of the inbred rats used in the inclined plane expcri- 



