312 SHINKISHI HATAI 



Semi-spaying produces neither an enlargement of the hypoph- 

 ysis, nor an abnormal fat deposition in the body. This is ex- 

 plained by the fact that the remaining ovary enlarges to twice 

 its normal size, thus we may conclude that the normal secretory 

 function is performed adequately by the tissues of the enlarged 

 ovary, and consequently the changes which would follow hypo- 

 secretion of the hypophysis are prevented. 



SUMMARY 



The conclusions here given apply to the domesticated albino 

 rat (Mus norvegicus albinus) and in the absence of direct evidence 

 should not yet be extended even to the wild Norway. 



1. Body weight. The growth of the body in weight is not 

 modified by castration or by semi-spaying. Spaying however 

 increases body growth, some of the increase in weight being due 

 to fat. 



2. The normal relation between body weight and body length 

 is not modified in the castrated or the semi-spayed. In the case 

 of the spayed, it is modified by the presence of fat; that is, the 

 animal is heavy for its body length. 



3. Tail length. The tail tends to be slightly longer in castrates, 

 but no alteration occurs in the other two series. 



4. Brain weight. In all series the difference between the oper- 

 ated and non-operated is almost negligible, nevertheless in all 

 the operated groups it constantly falls below that in the non- 

 operated. 



5. Spinal cord weight. In the castrated series the weight is 

 higher than in the controls, but follows the brain in the other two 

 series; the spayed and the semi-spayed. 



6. Percentage of ivater. The water .content of the nervous sys- 

 tem is not altered by any of the operations. 



7. Hypophysis. A striking and constant increase in the weight 

 of the hypophysis is shown after castration, but practically no 

 change after either spaying or semi-spaying. 



8. Ovaries. In the semi-spayed series the compensatory growth 

 of the remaining ovary is almost perfect and the single ovary has 

 therefore nearly twice its normal weight. 



