Abstract
While in cattle twins with anastomosing chorioallantoic blood vessels and in amphibians grafted together at an early embryonic stage sex hormones are exchanged in sufficiently large amounts to cause sex transformation, little, if any effect so far has been reported from experiments on parabiosis in fowl and in rats. This faces us with the double problem of the amounts of active hormones that may be transferred from one animal to its parabiotic twin and of the threshold values of the hormones considered. Witschi 1 states that the capillary connections in chains of a newt let pass enough of the hypophyseal hormones to stimulate the processes leading to metamorphosis, but too little to bring about the expansion of the melanophores.
From this it becomes obvious that the quantitative factor should be taken into consideration at the outset of parabiosis experiments. The author, therefore, has started some colorimetric studies on the amount and speed of exchange of blood in parabiotic rats. The technique developed by Dawson, Evans and Whipple 2 and by Smith 3 in their work on the blood volume of dogs has been adapted to the special conditions of our experiment.
One-tenth of a cubic centimeter of 1% Brilliant Vital Red (Evans) was injected into the heart of one of the twins. At the end of one hour samples of 3 to 4 cc. of blood were taken from both members of the pair, mixed with oxalate solution and centrifuged.
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