TIIK VESSELS. 49 



question merits an attentive observation, seeing tliat it 

 is very closely connected both with the ideas which we 

 must form of the nature of vessels in general, and of 

 their use. 



Mirbel, who first described ■«ith care these two kinds 

 of vessels, affirms that these marks are pores or holes, 

 commonly bordered by an opaque raised rim. He says, 

 in his Anatomie, torn. i. p. 57, that these pores are not 

 the 300th of a hne in diameter ; then, in his last work, 

 he reduces their diameter to nearly a third of that 

 which he first estimated them at, in saying that they 

 are perhaps not the 300th of a millimetre. He considers 

 the transverse Hnes of the annular vessels as a series of 

 closely approximated pores, and, consequently, as actual 

 slits. This opinion appears to have been admitted by 

 Bernhardi; and it is moreover maintained by Amici, 

 who gives a figure of these transverse slits (Observ. Micr. 

 fig. 31, 32). Kieser, although advocating a theory quite 

 opposed to that of Mirbel, admits likewise — 1st, that the 

 marks of dotted vessels are true pores, the orifices of 

 which he has seen in the Sassafras, the French Bean, and 

 the Oak. 2d, That the reticulated vessels present actual 

 holes formed by the incomplete junction of the spires. 

 Likewise he agrees with Mirbel upon the first point, 

 but differs widely from him in the second. That which 

 Amici says of the slits of the vessels, appears to relate 

 rather to the reticulated vessels of Kieser than to striped 

 vessels. 



On the other hand we find a great number of anato- 

 mists who deny the perforation of the marks of dotted 

 vessels. I have myself been induced by microscopic 

 observation to doubt the perforation of these organs, 

 and to believe that that which has been considered a 

 pore is a luminous spot, such as is seen in the bubbles 

 of air which are found in water in the field of the micro- 



VOL. I. E 



