1896-97.] Mr D. F. Harris on Living Animal Tissues. 
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Note on the Reducing Power of the Living Animal 
Tissues. By David Fraser Harris, B.Sc. (Lond)., 
M.B., CM 
(Read April 5, 1897.) 
The following demonstration of the avidity for oxygen on the 
part of the living animal tissues was made incidentally while I was 
injecting the gelatine and soluble Berlin-blue mixture (Ranvier) 
into the blood-vessels of cats and rabbits in preparation of histolo- 
gical material. If is a fundamental fact that living cells must have 
oxygen continually supplied to them ; the tissues crave oxygen, 
and will take it from any substance within their reach capable 
of yielding it (the inspiratory phase of the internal respiration). 
Normally the Hb0 2 yields it — the gas reaching the cells via the 
lymph. The left external jugular was chosen, and opened the 
instant the chloroformed animal’s heart ceased to beat : thus, 
though the animal was “ dead ” as a whole, its tissues were alive 
for varying periods thereafter. 
The fluid traversed heart and lungs before reaching the aorta 
and arterial circulation. On cutting up the organs I thought the 
injection must have “ failed ” in certain organs, for the kidneys 
and liver were markedly pale — pale green — and in some of the 
divisions of the portal vein the gelatine seemed uncoloured or 
“ bleached ” white. The lungs were of a deep blue ; and such 
organs as brain and eye were blue, while there was no loss of 
colour where the fluid and the blood had mixed in the vessels (in 
a case in which the blood had not been first washed out of the 
vascular system). Here we had clearly a case of de-oxidation of 
the deep blue ferric ferrocyanide (Berlin or Prussian blue) to the 
pale green or almost colourless ferrous ferrocyanide, which, how- 
ever, underwent re-oxidation on exposure to the air, for the blue 
colour returned progressively in from ten minutes to twenty-four 
hours after. Next morning, indeed, organs that seemed empty of 
injection showed full capillary contents. 
It is interesting that there was no reduction of the pigment on 
the part of the blood itself, and that the feeble metabolism in pub 
