334 E. R. HOSKINS 



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per cent for the older and younger groups respectively. Pos- 

 sibly pineal feeding retards growth of ovaries, but on account 

 of their great variability and the comparatively small number 

 of observations, there is considerable doubt as to whether the 

 decrease noted is significant. 



18. Testes {tables 5, 7, 9 and 10) 



a. Controls. In absolute weight, compared with Donald- 

 son's tables, the testes in my rats average slightly lighter (table 5) 



In relative (percentage) weight (table 9), in comparison with 

 the observations of Jackson ('13) on animals of corresponding 

 weight, the testes in my series appear relatively lighter in the 

 older group and of about the same relative weight in the younger 

 groups. Jackson's data included the epididymis, however, 

 and on this basis, with testis and epididymis combined, both 

 my old and young groups would appear to have heavier organs. 



b. Thyroid group. The testes of both sub-groups of the thy- 

 roid-fed males (table 9) show a slight increase in relative weight 

 as compared with the entire group of controls. This overgrowth 

 ranges from about 7 per cent in the group of older rats (in part 

 of which the dosage is very small and ineffective) to 13 per cent 

 in the young animals. Calculated by Donaldson's method the 

 older rats are seen to have testes of the same absolute weight 

 as the controls, and the younger rats to have heavier (10 per 

 cent) .testes than the corresponding controls. As in the case 

 of the ovaries, however, the testes show considerable normal 

 variability, and conclusions based upon a relatively small num- 

 ber of observations must be carefully guarded. 



c. Thymus, hypophysis, and pineal groups. In these groups 

 the testes show no important or constant changes in comparison 

 with the controls, and the differences (e.g., the apparent slight 

 retardation of the testis in pineal-fed) are probably not signifi- 

 cant. Microscopic examination of the testis of a thymus-fed 

 rat showed no degeneration, although Hewer ('14) found such 

 condition in rats, some of which were fed but slightly more thy- 

 mus than some of my rats received. (Mine were fed up to 1.4 

 grams fresh or 0.15 grams dried thymus on alternate days; hers 

 were fed 1 to 4 grams of the fresh thymus daily.) 



