In the search for a possible origin of some of the chronic and subacute illnesses of men in which there seems to be clinical evidence of a low grade intoxication, attention has recently been focused on the gastro-intestinal tract. In a previous paper, two of us with Cone1 reported the failure to obtain evidence of absorption of toxic substances from the normal intestine in dogs that had Eck fistulas and that were kept on a meat diet. We were then led to study the effect after a partial obstruction of the intestine. It became evident at once that it would be necessary, before going further, to study the altered anatomy and physiology as well as the changes in the bacterial content of the intestine resulting from this procedure. In the paper immediately preceding this,2 we have endeavored to indicate certain of the anatomic and physiologic alterations. In the