It is well known that hemorrhage causes fluid to enter the blood from the tissues. Likewise it is well known that colloid-free fluids on injection rapidly leave the blood and pass to the tissues. It was the object of this study to determine, if possible, whether certain tissues are of more importance than others in these interchanges. The experiments were carried out on cats anesthetized with ether. The tissues chiefly worked with were skin (clipped free from hair), muscle, intestine, spleen, liver and blood. Both kidneys were ligated off. Corresponding parts on each side of the body were prepared and when all was ready, the small pieces from one side were snipped off and dropped into stoppered weighing bottles. Then the experimental procedure was performed and after thirty minutes the corresponding pieces from the opposite side of the body were taken. The samples were all dried to a constant weight at 102°. The experimental procedure consisted in a hemorrhage of 15 cc. per kilo or in the injection of 25 ...