1877.] Sugar in relation to the Blood. 321 



employed in my experiments consists of an outer cell charged with bi- 

 chromate of potash dissolved to saturation in dilute sulphuric acid. In 

 this two carbon plates are immersed. The inner porous cell contains a 

 little mercury at the bottom, but is otherwise filled up with water. An 

 amalgamated zinc rod is inserted, and dips down into the layer of mer- 

 cury. This battery, it is found, gives a steady current, and, used every 

 day, will remain in good working order for at least a fortnight, all that 

 is necessary being to pour out the liquid in the porous cell when it has 

 become green from reduction of the diffused bichromate solution and 

 replace it with water. Attention is of course necessary to secure that 

 the proper battery-power exists to effect the deposition of the copper ; 

 and when the current becomes weak the zinc rod must be cleaned and the 

 bichromate of potash solution replenished. 



The relation existing between sugar oxidized and cupric oxide of the 

 copper test solution reduced is, that one atom of the former reduces five 

 atoms of the latter. This is the foundation upon which the action of the 

 test is based, and the calculation made in estimating by its agency the 

 amount of sugar present. Taking 63*4 as the atomic weight of copper, 

 and 180 as that of glucose (C 6 H 12 6 ), 317 parts of copper will stand- 

 equivalent to 180 parts of glucose. Thus one part of copper corresponds 

 to '5678 of glucose ; and in calculating the amount of sugar in the blood 

 analyzed, the weight of the copper deposited has only to be multiplied by 

 •5678 to give its equivalent in glucose. The quantity of sugar in the 

 amount of blood taken for analysis being thus determined, the data are 

 furnished by which the proportion per 1000 parts may be ascertained. 



I have entered thus minutely into the description of the gravimetric 

 process of estimating sugar, as I feel that it supplies a new mode of in- 

 vestigation which is calculated to materially advance our position with 

 reference to the physiological relations of sugar in the animal system. 

 It has hitherto always seemed to me that in giving numerical represen- 

 tations of minute quantities of sugar they could only be regarded as 

 approximate results. Xow, however, sufficient precision is attainable to 

 enable minute differences to be ascertained with the requisite certainty 

 for definite physiological conclusions to be drawn. 



In a further communication, to be presented for the next meeting of 

 the Society, I propose to give the results I have already obtained bearing 

 on (1) the natural state of the blood; (2) the comparative states of 

 arterial and venous blood ; and (3) the spontaneous change ensuing after 

 the removal of blood from the system. 



z 2 



