THE BLOOD SUGAR 649 



(6) Increased physical pciictnibility of tlie kidney membrane to 

 glucose. 



Both (5) and (6) arc hypothetical conditions, the latter having 

 been proposed as the basis of so called kidney diabetes, a state in 

 which glycosuria occurs with a normal or subnormal percentage of 

 sugar in the blood, in which the rate of sugar excretion is, in com- 

 parison with other forms of glycosuria, little influenced by the diet,'" 

 and in which the glycosuria tends to grow progressive!}' worse. 



THE BLOOD SUGAR 



The normal blood sugar concentration is found to average 0.10 

 per cent., but, as statistics show, it may vary at least between 0.06 and 

 0.11 per cent. The literature contains numerous references to that 

 blood sugar concentration which if exceeded leads to glycosuria 

 ("threshhold" value). In accordance with the general principles 

 above discussed we should expect this value to vary. It has been 

 placed at 0.147 to 0.164 per cent, by Foster, between 0.17 and 0.18 

 per cent, by Haman and Hirschman, at about 0.20 per cent, by Pavy, 

 and other writers have reported greater variations, due in part doubt- 

 less to differences in the analytical methods used. How widelj' the 

 threshhold blood sugar percentage may be varied by extreme variations 

 of the blood volume and other factors has not been settled. Following 

 the ingestion of free glucose the blood sugar percentage ordinarily 

 rises, and in a similar way, but more slowly, after feeding of starch. 

 Fisher and Wishart gave 50 gm. of glucose in 150 c.c. of water by 

 stomach to dogs weighing 8 to 9 kg. and found in the first hour blood 

 sugar percentages of 0.16 and 0.13. In succeeding hours there was 

 little variation from 0.11 per cent. In harmonj^ with the previous 

 work of Gilbert and Baudoin and the more recent studies of others on 

 man, these experiments showed that the blood sugar percentage rises 

 during the first hour, then falls and thereafter remains normal. There 

 was no increase of the blood volume during the first hour, the hemo- 

 globin percentage remaining unchanged, probably because the large 

 quantity of glucose in the bowel held water there. But in the second 

 hour the blood volume became large and the hemoglobin showed the 

 effects of dilution. In this same hour the sugar percentage returned 

 to normal. But the absorption of glucose was only completed in the 

 fourth hour and calorimetric observations by Lusk showed that the 

 metabolism also ran at a uniform* rate 20 per cent, above the basal 

 level into the fourth hour. Accordingly the observed blood sugar per- 

 centages first rose as the rate of sugar supply was increased, but fell 

 again during the maintenance of the increased supply and while the 

 metabolism was constant, owing to the shifting of water. 



When concentrated (54 to 72 per cent.) glucose solutions are in- 



5" Cf. Epstein;^ Strouse, Jour. Amer. Med. Assoc. 1914 (G2), 1301; Lewis and 

 Mosenthal, Johns Hopkins Hosp. Bull., 191G (27), 133. 



