THE PITUITARY BODY 



ocular region." In contrast to this view, Ivanowa (1935) be- 

 lieved that an important part of the effect is due to the action 

 of light on the whole body surface. According to Benoit 

 (1935), neither section of the optic nerves nor enucleation of 

 the eyes prevents precocious testicular growth caused by arti- 

 ficial light in the immature drake. Apparently the light had 

 to reach the empty orbits; for if hoods were placed over the 

 latter, testicular development was prevented. Experiments 

 like those just cited indicate the urgent need for more obser- 

 vations on the afferent pathways of reflex photostimulation 

 of the pituitary in birds. Ivanowa's experiments are open 

 to the objection that the birds' eyes may not have been ade- 

 quately hooded. It is difficult to believe that there is an im- 

 portant peripheral afferent arc other than the optic nerve. 



Benoit (1935-37) has made a number of other observations 

 in drakes either immature or during the period of normal 

 regression of the testis. (The effects on the gonad of the fe- 

 male are slight and appear much more slowly.) The testicular 

 response depends not only upon the duration of illumination 

 but also upon the wave-lengths (quaHty)" used and the dis- 

 tribution of "light-dosage." Testicular growth ceases if, dur- 

 ing artificial illumination, the drake's anterior pituitary is 

 removed. The gonadotropic potency of the drake's pituitary 

 in immature mice may be increased if the hours of illumina- 

 tion are experimentally lengthened. Such experimental de- 

 velopment of the testis and penis, for some weeks at least, 

 was found to be lessened greatly by thyroidectomy. How 

 thyroid deficiency acts, whether by interfering with secretion 

 by the stimulating organ (anterior pituitary) or by diminish- 

 ing the response of the end organ (testis), is not clear. The 

 feeding of thyroid extract or the injection of thyroxine acceler- 

 ates the rate of testicular growth. 



Light has been shown to influence greatly the development 

 of the gonads or secondary sexual characters including be- 



■^ In one report, Benoit states that red and infrared radiations are especially 

 effective. 



I60I 



