52 
ZOOLOGY: R. PEARL 
A parallel experiment to that reported above has been run with male 
birds, and gave essentially the same results. Since the numbers used 
were too small to give reliable figures, they are not pubHshed. 
Leaving now the matter of growth in body weight we may turn to a 
consideration of the attainment of sexual maturity in these three lots 
of birds. There was practically no difference between the three lots of 
birds in respect to time of beginning laying. The small differences ex- 
hibited cannot be regarded as significant, considering the nature of the 
character. 
Several interesting points are brought out by this experiment. In the 
first place the results with pituitary body substance confirm all of our 
earlier work with this substance so far as concerns activation of the 
ovary. There is no evidence that the administration of pituitary sub- 
stance hastened in any way the initial activation of the pullet ovary. 
The pituitary birds did not in fact begin to lay as soon as those receiving 
corpus luteum substance, though the two day difiference between the 
lots cannot be regarded as significant. We have now tested the effect 
of pituitary (anterior lobe) substance on the ovary in three different 
physiological states, viz., {a) completely resting adult ovary during 
moult, {h) adult ovary in laying condition but with declining fecundity' 
rate, and {c) the inactive, immature ovary of the young pullet. In 
none of these physiological states has there been the slightest evidence 
that the pituitary has activated or accelerated the activity of the ovary 
in any manner or degree. 
In the second place it appears that both pituitary (anterior lobe) sub- 
stance and corpus luteum substance retard growth in the chick, but 
without affecting the attainment of sexual maturity (egg laying) . The 
pullets in lots A and B began to lay at the same time they would have 
had they not received organ substance, but their body weight at the 
onset of laying was from 4 to 9% smaller than it would normally have 
been. These results are of interest in connection with the experiments 
of Gudernatsch^ in feeding thyroid and th3Tiius substance to growing 
tadpoles, though there is no evidence in the present experiments of 
differentiation being accelerated. It merely is not retarded, while body 
growth is retarded by pituitary and corpus luteum substance. It will 
be a matter of much interest to extend the period of feeding these sub- 
stances, particularly corpus luteum, into earlier life. I propose to do 
this next year. For students of growth a means is afforded in corpus 
luteum feeding of notably retarding body growth without disturb- 
ing, so far as yet appears, the normal physiology or physiological 
development. 
