A note on the parabiosis of rats and mice. 1

This study includes 50 parabioses between rats and mice, twenty of which were terminated before the fifth day by the death of one of the animals, usually the mouse. That is, only thirty lived sufficiently long to admit of a union, or to determine if a union would take place. Of this number twelve showed a more or less complete tissue connection. One pair lived twenty-eight days, but the majority died between the seventh and fourteenth days. This compares favorably with the mortality observed where mice alone were used.

The technique employed consisted in a peritoneal anastomosis from 2 cm. to 3 cm. long, and a skin muscle apposition for about double this distance. Young rats weighing about forty grams were used, with “growing” mice from a large breed. Additional sutures through the skin of the shoulder and neck and adhesive plasters about the body gave sufficient fixation.

The existence of a true anatomical union is based on: (1) histological studies; (2) recovery in a second animal of substances injected into the first; (3) hemorrhage from one animal through the dead tissues of the other (noted twice).