THE INHERITANCE OF PRODUCTIVITY IN FARM LIVE STOCK.      291

of an animal are to be expressed. Apart from nutrition, perhaps the most striking
effect on egg-production derived from control of extraneous environmental in-
fluence is that which follows increased exposure to light.

Just as we have a measure of the intensity of inheritance from observations
on parent and offspring in breeding practice, so to determine quantitative effects
of environmental factors on gene expression, it is necessary to have stock whose
genetical constitution is known.

There is yet another phase of genetical inquiry that may perhaps be con-
sidered of mainly academic interest, but from which we now have indications
that it may lead shortly to more practical and less tedious methods of controlling
heredity than that outlines earlier in this paper. In the final genetical analysis
the gap in our knowledge which exists between the presence of the gene, on the
one hand, and the exhibition of its end-product—the character—on the other hand,
must be bridged.

Hammond [ 7 ] has given us a suggestion as to the type of mechanism that
may lie between the genes and their characters. In the experiments on the
increased productivity due to an increased light ration, it is his opinion that
light acts by stimulating the anterior pituitary gland to increased secretion,
and this substance circulating in the blood stimulates in turn the ovary
to increased production. He further suggests that the level of this substance
in the blood may explain the difference between high and low egg-producing
strains and breeds.

It would be interesting to determine which of the five qualities outlined
previously as leading to increased egg-production are likely to be affected by
this stimulus.

Early sexual maturity.—The relation existing between sexual maturity
and the anterior lobe of pituitary is too well known to need labouring but the
work of Domm [ 8 ] in Chicago merits a brief notice. By suitable injections of
a preparation of this gland, he was able to produce precocious development in
the sex glands and secondary sexual characters of fowls, so that some of his male
chicks were crowing nine days after hatching, and began to tread when only a
fortnight old.

Persistency.—The length of time a bird continues laying after the production
of her first egg is limited by the time of appearance of the moult. In one of our
birds we were able to eliminate the moult by implanting anterior pituitary glands
from other birds (Greenwood [ 9 ]).

Broodiness.—From extracts prepared in our laboratory, Professor F. A. E.
Crew has been able to produce the typical behaviour of broodiness in Leghorn
fowls, a breed in which it rarely occurs. Even young hens reacted to the stimulus
before sexual maturity was reached.