Abstract
In a previous paper the author has described a method for testing the amount of blood exchange in parabiotic rats. 1 A large series of twins show that an average of 24% of dye is found in the uninjected animal at the end of one hour. Normal parabiotic female rats thus tested for their vascular connections come to maturity independent of each other. There is sufficient oestrus producing hormone exchanged to disturb slightly the cycles of each twin member, but not enough to synchronize them. The finer individual differences of each pair, according to a higher or lower amount of blood exchange are still under investigation.
In a series of 11 pairs in which the oestrus cycles had been followed over a long period, both ovaries were removed from one female. The castrate subsequently goes into anoestrum and only occasionally shows signs of oestrus while the normal female co-twin has normal cycles. This agrees with the above mentioned fact that there is little interference of oestrus in pairs of normal females. Our results vary from those of Martins, 2 who describes the production of oestrus in a castrate member by carry-over of hormones from the normal co-twin. The rats he used were put in parabiosis with the body cavities joined (coelioanastomosis). In this condition it is possible that some hormone exchange may take place also through the medium of the peritoneal fluids and not exclusively through the blood. To check this we have followed the cycles of 9 pairs, one member a castrate, in which the body cavities were not connected, and of 2 pairs in which they were in open connection. At present no difference has been noted between the 2 conditions.
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