304 PRACTICAL MICROSCOPY. 



A suitable cell must first be selected, one of brown 

 varnish in this instance, and filled with the carbolised water 

 just made milky with the starch. The thin glass cover 

 having been taken up on the end of a pencil as already 

 described when mounting diatoms by the dry method, is 

 edged with brown varnish, allowed a few minutes to nearly 

 set, and then placed in contact with the cell but not pressed 

 down in the centre to any extent. The superfluous fluid 

 may then be absorbed with blotting paper, the slide placed 

 on the turntable, and another coat of brown varnish applied 

 to the edges. Put aside now for a day or more, and then 

 finish with white zinc varnish or asphaltum according to the 

 taste of the operator. 



If the student possesses an air-pump he will find that fluid 

 mounts will be rendered more permanent by placing the 

 cell filled with fluid under the receiver so as to eliminate 

 the air which most liquids contain. The best form of air- 

 pump has been shown at Fig. 222, but there are other forms 

 which, though not so generally useful, are nevertheless 

 handy on account of their small size. One of these is 



shown in Fig. 249, from which it 

 will be seen that it is capable of 

 taking slides only. 



Many other fluids may be used 



in place of the carbolised water: 

 FIG. 249. 



the cuticle of esparto grass is 



shown very well when mounted in dilute acetic acid, the 

 fibres of jute exhibit the ladder-like markings to perfection 

 when put up in dilute spirit, whfle many of the desmids 

 and minute algae can only be kept in distilled water in 

 which a lump of camphor is kept. Some of the smaller 

 organisms may be put up in a very dilute solution of osmic 

 acid. This plan is advised by Mr. Saville Kent for the 

 preservation of the collared monads, in his ' Manual of the 



