The immediate effect of the operation on the portion of the kidney remaining is an infarcation of the tissue compressed by the sutures. This area of necrosis extends but a short distance into the adjacent kidney tissue. The infarcated tissue gradually becomes replaced by fibrous tissue and in three to four week's time the necrotic tissue entirely disappears. The amount of fibrous tissue in time becomes so slight and the healing so perfect that it is difficult to detect the site of the operation. The renal elements sometimes persist in the infarcated area and the glomeruli apparently are more resistant than the tubules. The tubules in the infarcated area sometimes become calcified and bone formation beneath the epithelium of the pelvis is of very frequent occurrence. The pelvic epithelium usually shows marked proliferation and may invade the field of operation in alveolar masses. Calculi may form in the pelvis of the kidney. Sutures penetrating the pelvis as well as the necrotic tissue resulting from the compression of the sutures probably furnish the nuclei for the calculi.

Removal of approximately half of one kidney did not alter either the remaining portion of that kidney or the size of the opposite kidney in two animals of this series. These experiments were terminated on the thirty-fourth and forty-seventh days. In a similar experiment of twenty-one day's duration there was slight but definite atrophy of the remaining tissue of the kidney operated upon.

Removal of approximately half of each kidney at one operation did not alter the remaining kidney tissue in two animals of the second group. The longest period of observtaion was fifty-four days. On the other hand in a similar experiment where 164 days elapsed, the remaining portions of each kidney had increased markedly in size.

Removal of one kidney and approximately half of the other did not alter the remaining kidney tissue in six animals in which from five to fifty-six days elapsed before termination of the experiment.

In six experiments in which one kidney was removed and approximately half of the other, three of the animals died as a result of the operation on the sixth, seventh and tenth days. The probable cause of death was renal insufficiency: the animals refused food, vomited persistently and lost strength and weight. The other three animals recovered and were killed at periods varying from five to eight weeks. The reduction of the kidney tissue to one quarter of its original amount at one operation was attained with danger but was not necessarily fatal.

In every experiment there was a loss of weight varying from four to twenty-four per cent. To what extent this loss in weight is due to the reduction of kidney substance and to what extent it is due to diet and confinement it is impossible to say, as we made no control experiments to elucidate these points.

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