ENDOCRINE SYSTEM 165 



change in the nature or the distribution of the refractive sub- 

 stances aside from the solvent water. This change is in the 

 same direction and of approximately the same degree in the two 

 sexes. 



Effect on reproduction (Hammett, '22). Studies have been made 

 of the reproductive ability of thyroidless albino rats. It was 

 found that conception occurred when male "thypars" or "para- 

 thys ; ' were mated with female "thypars" or "parathys." 



When the thyroid apparatus was removed from young rats 

 45 or 56 days of age, there was no apparent inhibition of function 

 of the internal secretion of the gonads (stimulation to develop- 

 ment of the secondary sexual characteristics; stimulation to 

 sexual activity; preparation of the uterine mucosa for nidation). 



The formation, maturation and discharge of the gametes were 

 however disturbed by the loss or deficiency of the thyroid secre- 

 tion, as were the reproductive processes subsequent to gonadal 

 participation. This is shown by the increased sterility, greater 

 age at breeding, high birth mortality, high mortality during and 

 after weaning, the smaller number of rats in the litters, and the 

 failure of the rats to thrive during the nursing period, as do the 

 young of normal mothers. 



13. Pineal gland. See References. 



14. Hypophysis. The influence of diet on the extracts of the 

 hypophysis and the thyroid, tested against the intestinal strip, 

 was studied by Degener ('22). The diets used were oatmeal, 

 vegetables (fresh), meat and the standard diet plus potassium 

 iodide. The extract of the entire control hypophysis causes a 

 relaxation of the strip; with the oatmeal and vegetable diets it 

 causes a contraction. In the controls the extract of the glandular 

 portion alone causes contraction, that of the nervous portion 

 alone, relaxation. The experimental diets which are effective 

 produce an extract of the entire gland similar in reaction to 

 that of the glandular portion alone. 



The extract of the thyroid gland was not modified in its action 

 by diet. 



Excitement and starvation. The effect of general excitement or 

 fighting on the secretion of the several ductless glands, as indicated 



