MICROSCOPIC ILLUSTRATIONS. 



stem c, turned a quarter round, where it is firmly clasped 

 by the screw z. The body and arm, a, g, is drawn out 

 by turning the pinion-head s, so as to admit of the phial- 

 holder h, being placed in its situation. This piece of 

 apparatus is shewn separately on a larger scale at fig. 22, 

 where p, p, are meant to represent the pins by which it 

 is attached to. the microscope. Within the tube o, slides 

 another, s, which is propelled by a helical spring inserted 

 within it. This latter, or sliding-tube, has a thin con- 

 cave plate in front of it. When a phial, or other glass 

 vessel, similar to that shewn at fig. 23, is to be inserted 

 into the phial-holder, the tube s must be drawn back 

 towards o ; when liberated, the vessel will be firmly held 

 in any position. 



Fig. 22. 



Fig. 23 illustrates the method by which an aquatic 

 plant is mounted, to exhibit the circulation. The plant 

 is carefully laid along the inside of the vessel, which is 

 empty. A slip of glass, , is then covered over it, with suffi- 

 cient care to prevent it being injured. A small piece of 

 cork, by is fitted behind it, and the vessel, then placed in 



