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The sugar poured into the general circulation through the hepatic 

 veins is conveyed to the capillaries of the lungs, where it in great part 

 disappears, but never entirely so, according to very numerous analyses 

 which the author has made on this subject. If the blood be traced 

 onwards from the arteries through the systemic capillaries into the 

 veins, the small amount of sugar which impregnates arterial blood 

 will be found to be still undergoing a process of destruction ; and 

 what appears exceedingly interesting, this process of destruction is 

 not carried on with equal activity in the different parts of the 

 system at large. In the capillaries of the chylo-poietic viscera, the 

 destruction is so complete, that the blood in the portal vein may be 

 entirely free from saccharine principle, when the blood returning 

 from other parts, as that contained in the femoral or jugular veins, 

 remains slightly impregnated. This curious fact has a bearing that 

 will be presently adverted to, with reference to the views to be 

 advanced concerning the nature of the metamorphosis of sugar in 

 the animal economy. 



The principal seat of destruction of saccharine matter in the 

 animal system being located in the respiratory organs, seems at first 

 sight to support the theory of Liebig that sugar is one of those sub- 

 stances which undergoes a process of combustion, by its direct com- 

 bination with oxygen and its resolution into water and carbonic acid. 

 Some experiments on the temporary obstruction of the respiration 

 and the examination of arterial blood before and after the operation, 

 led the author to call in question this view, as he observed that 

 notwithstanding the supply of oxygen was cut off to such an extent 

 as almost to occasion death, yet a considerable destruction of sugar 

 took place in the lungs. This, coupled with the fact that a disap- 

 pearance of sugar takes place in the systemic capillaries, and un- 

 equally so in different portions of then^ induced him to push his 

 investigations, and see if there might not be some other cause in 

 operation in the living animal to effect the normal destruction of 

 sugar, besides the direct chemical action of the oxygen absorbed in 

 respiration. The results of these investigations, which were first 

 directed towards the changes produced in blood normally containing 

 sugar, injected through the capillaries of lungs removed from the 

 animal, and artificially inflated with atmospheric air or oxygen gas, 

 have induced the author to, refer the metamorphosis of sugar in the 



