The effects of semi-spaying and of semi-castration on the sex ratio of the albino rat (Mus norvegicus albinus) / Helen Dean King.

  • King, Helen Dean, 1869-1955.
Date:
1911
Catalogue details

Licence: In copyright

Credit: The effects of semi-spaying and of semi-castration on the sex ratio of the albino rat (Mus norvegicus albinus) / Helen Dean King. Source: Wellcome Collection.

Provider: This material has been provided by The Royal College of Surgeons of England. The original may be consulted at The Royal College of Surgeons of England.

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    inbreeding experiments, and it is well known that inbreeding causes a marked decrease in the number of offspring. A normal sister of two of the semi-spayed rats was mated four times to a normal male. She had a total of 24 young, of which fourteen were males and ten were females. The average number of indi- viduals to a litter in this instance was six. One of the females operated upon by Doncaster and Marshall gave birth to a litter of seven young; but none of the semi-spayed rats used in these experiments ever had a litter containing more than six individuals. It seems probable, therefore, from the data shown in table 2, that semi-spaying causes a decrease in the average size of the litters, although it has no appreciable effect on the sex ratio, and apparently does not decrease the number of litters a female can produce. Two of the semi-spayed females used in these investigations died from pneumonia; the other two were etherized when it became evident that they were out of condition and would not breed again. An autopsy was made in each instance, and in no case was there any ovarian tissue on the side of the body that had been operated upon. The remaining ovary appeard normal in every female, and there was no marked increase in its size to compensate for the loss of the other ovary, as Doncaster and Mar- shall found to be the case in each of the two rats upon which they had operated. As these investigators operated upon adult rats and killed them about two months after the operation, it seems probable that the noticeable increase in the size of the re- maining ovary must have been due to some pathological condi- tion, and not to a normal ‘compensatory hypertrophy.’ There is a considerable variation in the size of the ovaries of the same rat, as well as in those of different rats; and it is not improbable that the same ovary varies in size at different times. A series of careful measurements would have to be made of a number of ovaries, removed from females at different times in the month and at different seasons of the year, in order to obtain proper standards by which to measure any apparent deviation from the normal size.