8 4 



PRACTICAL MICROSCOPY. 



amongst the fibres, is kept comparatively still, by which its 

 form can be clearly made out. 



Two forms of cages or live-boxes are shown in Figs. 70 

 and 71. They are, however, not all that can be desired. 

 Just so much pressure must be applied to the cap as is 



necessary to keep the 

 animal still, and no more, 

 or it will be crushed and 

 distorted, so that the cap 

 requires much dextrous 

 manipulation. Often- 

 times such objects as 

 Entomostraca, &c., will 

 FIG. 70. not display themselves 



to adVantage, so that the 



cap requires loosening, to be again squeezed down at an 

 opportune moment. Moreover, it is generally found that 

 some particular organism will get near the periphery of 

 the cover, and in this all the interest may be concentrated, 



yet the objective will 

 not reach it if it happens 

 to be of the form of 

 Fig. 71, and if we adopt 

 the form of Fig. 70 we 

 are often precluded from 

 using the achromatic 

 condenser to any portion 

 but the centre of the 

 slide. Instead of this 

 we may use the compressorium as made by Messrs. Beck, 

 Ross, Collins, and others, for use with high powers ; but 

 Piper's form, made by Mr. Swift, and illustrated in Fig. 72, 

 will be found more convenient. 



The most delicate pressure can be applied by means of 



1 



FIG. 71. 



