ZOOLOGY AND BOTANY, MICROSCOPY, ETC. 



713 



Fig. 137. 



Fig. 139. 



microtome should be ground flat. This Dr. S. Marsh considers to be 

 a most unsuitable arrangement, as a very little actual experience of 

 section-cutting will speedily demonstrate. After many unsuccessful 



attempts to obtain a really good and 



reliable section-knife, he had one 



made, which has proved everything 



that could be desired. 



The knife is shown in Figs. 137 



and 138, the latter being a trans- 

 verse section of the blade. It is fur- 

 nished with a blade 4: inches long 



and |- inch broad, set in a square 



handle of boxwood, also 4 inches in 



length. The thickness of the blade 



at the back is not quite a \ inch, 



while both of the surfaces are ground 



slightly hollow. It is essentially 



necessary that the back and edge of 



the blade be strictly parallel to each 



other ; that is to say, the edge must 



form a straight line, and both the 



edge and under side of the back must 

 Fig. 138. li e i n the same plane, otherwise the 



knife, when in use, will have such a 



tendency to tilt over as to render its 



management extremely difficult. It 



is very easy to discover if this con- 

 dition be fulfilled, for if, on care- 

 fully laying the flat of the blade 



upon a piece of level glass, every 

 portion of both back and edge are found to be 

 in close contact with it, the knife may in this 

 respect be considered perfect. 



Thanhoffer's Irrigation Knife.* — This 

 (Fig. 139) devised by Professor L. v. Than- 

 hoffer, and adapted either for free-hand cut- 

 ting or with a hand microtome, consists of a 

 blade (wedge-shaped in section) 11 cm. long 

 and 2 5 cm. broad, a handle 12^ cm. long and 

 li cm. broad, and a tube (a b) for sup- 

 plying water to the blade. This tube is 

 attached to the back of the blade, and is there 

 pierced with a row of fine holes ; it also 

 traverses the handle and terminates at its butt- 

 end in a tap, to which an indiarubber tube 

 may be attached. The fixed tube is supplied by the indiarubber 

 feeding-tube with water from a vessel placed on a higher level or 

 from a water-main. The water comes out of the small holes in drops 



b 



Arch. Mikr. Anat., xix. (1881) pp. 315-7 (1 fig.)- 



