Lane-Claypon and Starling also found that removal of both ovaries in the rabbit before the fifteenth day was apt to cause abortion, but at a later stage the same operation could be performed without interfering with the course of pregnancy. According to these authors numberless instances prove that in women double ovariotomy does not necessarily interfere with the course of pregnancy or the development of the milk glands. Parturition may take place and be followed by normal lactation. This shows that a hormone from the corpora lutea is not necessary either to the uterus or the milk glands, at any rate in the last third of pregnancy, though of course this does not prove that such a hormone is not necessary for the earlier stages both of pregnancy and growth of the milk glands. The results of Steinach, if confirmed, would prove conclusively that the ovaries and testes produce hormones which determine the development of all the sexual characters, not merely physical but psychical. He adopts the view that the interstitial cells or gland are the source of the active hormone. He claims by transplantation of the gonads in young rats and guinea-pigs to have feminised males and masculised females. The females are smaller, and hare finer, softer hair than the males. The testes were removed and ovaries implanted in young males. The animals so treated grew less than the merely castrated specimens, and therefore when full-grown resembled females in size. In the young state both sexes have fine, soft hair, the feminised males had the same character, like the normal females. They also developed teats and milk glands like the females, and were sought and treated as females by the normal males. When the implanted ovaries are able to resist the influence of their new surroundings, the female interstitial gland, which Steinach calls the puberty gland, develops so much that an intensification of the female character takes place: the animals are smaller than normal females, the milk glands develop and secrete milk, which can be easily pressed out, and if young are given to them they suckle them and show all the maternal instincts. Why the ovary in normal circumstances only when in the gravid condition calls forth this perfection of femaleness is to be shown in a later publication. By acting with Röntgen rays on the region where the ovaries lie, Steinach and his colleague Holzknecht brought about all the symptoms of pregnancy, development of teats and milk glands, secretion of milk, and great growth of the uterus in all its layers.