United States or Maldives ? Vote for the TOP Country of the Week !
This does not, however, agree with the result of removal of the ovaries in ducks, for this causes the characters of the male to appear, so that the dominance of the female is not a permanent condition of the soma but is dependent on the ovarian hormone. In the hermaphrodite individuals mentioned above the difference of dominance is on two sides of the body instead of two different individuals.
Pottenger earned his daily bread performing a rather simple task, assaying the potency of adrenal hormone extracts. At that time, adrenaline, a useful drug to temporarily rescue people close to death, was extracted from the adrenal glands of animals. However, the potency of these crude extracts varied greatly.
In addition to this function, the interstitial cells by their hormone also give the sexual character to the soma. When castration is carried out at birth the male somatic characters do not entirely disappear, because the hormone of the interstitial cells has acted during intrauterine life. In the embryo the interstitial gland is large, in the adult proportionately small.
Scattered here and there among the definitely glandular cell groups creating the external secretion are smaller collections of cells, called the islets of Langerhans, which have been demonstrated to elaborate the internal secretion. There are about a million of these islands in each gland. The hormone has been called insuline.
The factor in the gametocytes then in each generation acted upon by both hormones, and we must suppose that in some way the result was produced that the hereditary development of the antler in the soma only took place when the testicular hormone was present.
But having the precursors present is not enough. Growth hormone is only manufactured under certain, specific circumstances: for about one hour immediately after going to sleep and then only if the blood supply is rich with argenine and ornithine but contains few other amino acids; it is also manufactured during heavy aerobic exercise that goes on for more than thirty minutes; and growth hormone is produced at an accelerated rate when fasting.
It is not even certain that the black or white hair or feathers are giving off special hormones which would or could influence the gametes. The hormone theory only postulates such influence from hormones issuing from tissues modified by external stimuli. It is quite certain that the black colour in Leghorns or guinea-pigs is not due to any external stimulus or influence.
When the head begins to form in the process of individual development, the factors, according to my theory, have a tendency to form the special growth of tissue of which the incipient antler consists, but part of the stimulus is wanting, and is not completed until the testicular hormone is produced and diffused into the circulation that is to say, when the testes are becoming mature and functional.
I do not think it is necessary to suppose, as do Lane-Claypon and Starling, that the hormone physiologically inhibits the dissimilative process and augments the assimilative, and that the withdrawal of the hormone at parturition therefore causes the dissimilative process, i.e. secretion of milk.
What we have to consider and to investigate is whether the legs arose as a gametic mutation or as a direct result of locomotion on land. The general result of clinical and experimental evidence is to show that the hormone of the thyroid is necessary to normal development.
Word Of The Day