SECT. I. WOUNDS. 483 



this bark ; and in the following year a new ring of 

 bark was generated concentric to the former, and 

 also a new layer of wood beneath it ; and so on suc- 

 cessively, approaching the centre of the wound, till 

 at last the whole area was covered, but without any 

 actual union of the old and new wood. Such then 

 is the process of nature in healing up wounds of 

 this kind when left exposed to the air. 



But the result is not the same when the wound is 

 covered from the air. In the season of the flowing 

 of the sap Du Hamel detached a ring of bark, of 

 three or four inches in breadth, from the trunks of 

 several young Elm- trees, taking care to defend the 

 decorticated part from the action of the air, by 

 surrounding it with a tube of glass cemented above 

 and below to the trunk. After a few days the tubes 

 became cloudy within, particularly when it was hot ; 

 but when the air became cool, the cloud condensed 

 and fell in drops to the bottom. At last there be- 

 gan to appear as if exuding from between the bark 

 and wood of the upper part of the wound, a sort of 

 rough scurfy substance ; and on the surface of the 

 wood, as if exuding from between the longitudinal 

 fibres of the alburnum, a number of gelatinous 

 drops. They were not connected with the scurfy sub- 

 stance at the top, but seemed to arise from small 

 slips of the liber that had not been completely de- 

 tached. Their first appearance was that of small 

 reddish spots changing by degrees into white, and 

 finally into a sort of grey, and extending in size till 



2 i 2 



