Doses of 5 and 10 units of insulin have exerted little effect on the glycosuria in several such cases. This observation with variations, made on a number of cases showing no sharply definable tolerance limit, suggests the possibility of using insulin in differential diagnosis.
Determining the Value of a Given Preparation of Insulin: Individuals who have long suffered from severe diabetes and who for a period of years have not under any circumstances developed more than a certain maximum tolerance afford the most favorable medium for accurately gauging the number of grams of glucose that will be thrown into utilization by a given volume of insulin solution. Individuals whose glucose tolerance is known to be subject to fluctuation in response to factors other than insulin administration are not suitable cases to employ for the purpose of standardizing preparations. Again, early or mild cases of any kind are not dependable because if they have fixed or relatively fixed tolerance limits there is no way of demonstrating this except by the passage of time. Complete or nearly complete de-sugarization of the urine in any case of diabetes may be and commonly is followed by a lesser or greater increase of natural tolerance whether the desugarization be effected by diet adjustment alone or diet adjustment plus insulin. Hence if a certain diabetic individual on a fixed diet be excreting steadily 10, 20 or 30 gm. of sugar in the urine daily, and if after receiving a certain volume of insulin solution he pass urine that is sugar "free" or nearly so, it does not follow that the insulin injected has accounted directly and per se for all of the glucose that has disappeared from the day's urine. The desugarization or radical reduction of circulating sugar may result in a rising production of insulin from endogenous sources, and this endogenous insulin by adding its effect to that of the insulin actually injected from without may make it appear that the latter has a greater potency than it actually has. With these considerations in view it has seemed appropriate to select with great care for standardizing purposes old cases with long metabolic records, whose tolerances have long remained fixed or relatively fixed at low levels. Such cases have then been placed on regimens which permit them to excrete steadily 20 to 30 gm. of sugar per day. They have then been given doses of insulin that reduce the sugar excretion definitely but without approaching complete desugarization. If 10 units of a preparation given under such conditions lowers the