VOL. XXXr.] PHILOSOPHICAL. TRANSACTIONS. 505 



length of tlie wood, and which appeared of such a size in the microscope, 

 that one would have judged a pea might pass through them. Where the wood 

 looked reddish, I found these large vessels filled with a substance of a fine red 

 colour; so that I imagined these great vessels carried a red sap into the hori- 

 zontal vessels, which appeared so very numerous, and so thick together, that 

 they caused the wood to appear of the same colour with the red substance con- 

 tained in them. 



I afterwards cut off some very thin slices transversely from this wood, and 

 putting them into a China cup, I poured some hot water on them, and suffered 

 them to lie in it for some time; then viewing them with a microscope, I ob- 

 served that the red substance was extracted by the water, and no red colour was 

 now to be' found in any of the vessels. 



What seemed most surprising was, that cutting through the wood lengthwise, 

 as I frequently did, I observed it to be of a fine red colour for a hair's breadth, 

 and a hair's breadth farther it appeared white; and the ascending vessels seemed 

 to be smaller where the wood was red than where it was white; which nar- 

 rowness of the red vessels I judged to proceed from the sap contained in them. 



In viewing the ascending vessels in oak, I found some other vessels which 

 entered into their sides, and appeared like so many small round holes, especially 

 where the horizontal vessels lay, which I judged to be united to the ascending 

 vessels by means of those small orifices, and thereby to discharge part of their 

 sap into them. 



Taking a small twig of an oak, which in 7 years growth was about the thick- 

 ness of a finger, I cut it through lengthwise, both of the ascending and hori- 

 zontal vessels, which last I saw lying in great numbers very close together, and 

 proceeding directly from the pith of the twig. 



I have likewise made some observations on fir wood, in which the ascending 

 vessels consist of so very fine and thin a substance, that they exhibit a very 

 delightful spectacle in the microscope. In these ascending vessels I imagined 

 that I saw some globules, with a small opening in their middle, which seemed 

 to be of a closer and denser substance than the rest of the wood. But I after- 

 wards found myself mistaken, and that these supposed globules were nothing 

 else but the orifices, by which the ascending and horizontal vessels were united 

 together, and through which the sap was carried from the one to the other. 



From these observations I turned my thoughts to the fleshy fibres of animals, 

 and began to consider that, since the Author of nature usually observes the same 

 frame and structure in a great variety of his creatures, perhaps the fine mem- 

 branes, with which every muscular fibre is invested, and which are provided 

 with an innumerable multitude of small vessels, might carry nourishment in the 



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