1355 
looked for in the action of the entire surrounding tissues, which, in 
the case of the eye-chamber, will fairly certainly show a smaller 
metabolism than the cerebral tissues with which the cerebro-spinal 
liquid is as much in interaction as it is with the blood. 
A somewhat rapid sugar-consumption in the cerebral-tissues will 
necessarily cause a continuous diffusion of glucose from the cerebro- 
spinal liquid to this place of lower sugar-concentration. The quantity 
of sugar in the cerebro-spinal liquid therefore remains constantly 
lower than its value would be if it had interacted only with the 
blood; lower also than is found in the chamber-liquid. Thus we 
may expect for the same reasons that the blood itself will yield 
more sugar in the brain than round the eye-chamber and that, 
therefore the blood in a cerebral vein will show a greater decrease 
in sugar-percentage than the blood flowing from the eye-chamber 
and its surroundings. 
A comparison of the ultra-filtrates of the blood from the a. carotis 
and the v. facialis posterior taught us that the difference in sugar- 
percentage between arterial and venous blood is almost completely 
due to the free sugar, while the quantity of ‘combined sugar” 
suffers hardly any modification ip passing the capillary tubes. 
It looks tempting to suppose that the combined sugar plays a 
part in the consumption of the sugar in the tissues: here the sugar 
would continually be combined (adsorbed?) and be combusted in 
that’ condition; this would continually cause the fixing of fresh “free” 
sugar from the neighbourhood; this would cause the decrease of 
concentration of free sugar on that spot, followed by diffusion from 
the blood, ete. A correct opinion about this supposition can only 
be pronounced when it is settled that the reducing substance, which 
cannot be ultra-filtrated, is sugar and when it is further settled of 
what kind the substance is to which this sugar is “combined”. 
SUMMARY AND CONCLUSIONS. 
We can sum up the results of our investigations as follows: 
1. In the case of rabbits the sugar-percentage of tissue-liquids con- 
taining practically no colloids (aqueus humour, cerebro-spinal fluid) 
is as a rule smaller than that of blood-plasm, investigated at the 
same time. This phenomenon is in agreement with the lower value 
for the sugar-percentage which ultra-filtrates of serum in vitro show 
when compared with this serum. 
2. As regards the liquid of the eye-chamber, this difference of sugar- 
percentage, compared with plasm of arterial blood, is the same as the 
