The report of Williams1 has stimulated interest in the possibility that heat labile bacterial toxins may play an important role in the toxemias of intestinal obstruction and allied disorders. The physical nature of the material obtained from the intestinal tract in these clinical or experimental conditions is such that it is extremely difficult to prepare a sterile filtrate which exhibits anything like the potency of the original material.Experiments were undertaken to determine whether the fluid from closed intestinal loops of dogs contained appreciable quantities of filterable heat labile toxins. The method of Berkefeld filtration was employed to obtain sterile material for injection into guinea pigs, rabbits and pigeons. A comparison was made of the toxicity of unheated Berkefeld filtrate and fluid heated to 65° C. for one hour and strained through glass wool. Filtration was extremely slow and the quantity of material available from each closed loop usually permitted only one toxicity test to be made.I...