i* 
BEPOET ON THE CAOUTCHOUC OF COMMEECE. 37 
interesting physiological operation in removing bark fronftiving 
Cinchona owes its success to the care taken in order to ensure this 
Cambium layer from injury. 
Ike only effect to provide in such an implement is that it 
should just remove or cut through sufficient bark to rupture the 
laticif erous vessels, situated principally in the middle or Mesophlceum 
layer of the bark, and thus allow the milk to escape. The very 
formation of such a tool should prevent the possibility of “ hacking ” 
or chopping through the bark. The Manna knives (Figs. 7 and 8) 
are good for their purpose, and Mr. Mann has sent me a knife 
(Fig. 9), 'Which had before suggested itself to me and which is 
B*CK. 
used in the forests of Hanover for marking standing timber, and 
in this country also for marking timber, and which I have found, 
when I had occasion to use it for some little time, exceedingly 
well adapted to the purpose. A similar knife is also used by 
farriers. The blade which* when open forms an obtuse angle with 
the handle, has its end bent round in a |J shape, the lower of it 
being the only cutting edge. If a few such blades of a larger 
size, fixed or fixable to long handles for reaching up the trunks 
of trees, were tried, I believe they would prove a good kind of tool 
to use. Certain modifications might be made, as possibly to make 
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