1. The reactions of the dog's liver to (a) thyroidectomy and (b) both hypophysectomy and thyroidectomy are described.

2. Fatty changes of varying severity were detected in 8 of the 9 hypophysectomized-thyroidectomized dogs, hepatic fibrosis in 7, and severe cirrhosis in 4 animals of this group.

Among the thyroidectomized animals histologically demonstrable fatty livers were present in all 8, mild fibrosis was observed in 4, while early and mild cirrhosis was diagnosed in only one dog.

3. Two pathogenetically distinct forms of cirrhosis were present in the livers of dogs with the two operations, namely (a) cirrhosis initiated and developing around the radicles of the hepatic veins, and (b) periportal cirrhosis.

Both forms of cirrhosis occurred in dogs that were subjected to the same experimental procedures, and both forms could be found in the same liver.

The pathogenesis of these two forms of cirrhosis is described.

4. The relation between fatty change in the liver and the genesis of fibrosis is discussed, and it is suggested that, while fatty change may facilitate the evocation of cirrhosis, this reaction on the part of the supporting and vascular elements of the liver is not solely dependent on the fatty change in the liver cells.

5. The relation between the endocrines and hepatic cirrhosis is discussed. Since cirrhosis was slight in the fatty livers of thyroidectomized dogs, whereas it was often advanced in hypophysectomized-thyroidectomized dogs, it is suggested that in the absence of the pituitary cirrhogenic mechanisms are facilitated in the dog.

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