circus movements of the heart. Such changes in impulse formation or conduction probably represent an imbalance between the various substrates and enzymes implicated in the release of energy through glycolysis, which is known to proceed over an intricate chemical pathway involving numerous stages. High concentrations of the effective sulfa drug may alter impulse initiation or propagation within the reticular gray matter of the medulla by disturbing the enzyme-substrate relationship in one or more stages, and in this way modify the development of the unstable chemicalnervous state necessary for "toppling."" I t is not clear why the drugs increase the anaerobic survival. I t is possible that depression of certain enzymes diminishes the rate 3IPdWI~l~, c. 7'. J f~l S l J~ [h, '-t, 1,0u1s. 1941, 1'. 55.7 -
D a d , I'., 3 f U C l C O d ' h ~/ l , l J~l O~~J~l /111 ~f l J t / C r / l of release of anaerobic energy and thus permits continued utilization of a limited amount of available fuel. However, the apparent increase in overall energy liberation would seem to speak for an enhancing action of certain enzyme systems and an increase in utilizable fuel.Nor is it clear why sulfanilamide and sodium sulfathiazole were effective in producing the results described while equivalent amounts of sodium sulfadiazine and sodium sulfamerazine were not.Summary. Sulfanilamide and sodium sulfathiazole in non-toxic doses prolonged the survival of the anaerobic activity of the respiratory center of young rats and increased the overall energy release. Neither sodium sulfadiazine nor sodium sulfamerazine acted similarly.
The excretion of xylose has been investigated as a further application of the method of analysis which we have already applied to the excretion of ingested creatinine (1). The method consists in analyzing separately the time change in the rate of excretion by the kidney and in the plasma concentration, after the initial disturbance produced by the rapid absorption of creatinine and its distribution in the body fluids has subsided. It was found that, in the case of creatinine, both the rate of excretion and the plasma concentration diminish exponentially in the course of time, the two functions being asymptotic to their pre-ingestion values, and furthermore, that the coefficients of the time in both exponentials are equal, on an average. Under these conditions, it was proved that the elimination of the time between pairs of simultaneous equations yields a linear relation between the rate of output and the instantaneous concentration in the plasma. It was also proved that the method provides the means of determining the errors of observation. After the constants had been calculated and the errors of observation taken into consideration, it was shown that practically all the variation in the ratio of the rate of output to the plasma concentration (called glomerular filtration rate (2) or creatinine clearance (3) ) could be accounted for.The growing literature on xylose has prompted us to study the excretion of this substance by the same method. The same interpolating functions have been found to hold as in the case of creatinine, namely, simple exponential functions of the time, asymptotic to the pre-ingestion blank levels. The only difference in the behavior of the two substances, outside the values of the constants, is that the exponential phase of decrease in plasma concentration (x) and rate of output (y) begins somewhat later after the ingestion of xylose than after creatinine. The two exponential curves will be referred to as the x curve and the y curve respectively.
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