74 THE MICROSCOPE. 



favour of the spontaneous generation theory, may pro- 

 bably be studied with some advantage. Not only are the 

 minuter atoms too small to be studied by the T ^th or i^th, 

 but particles too transparent to be observed by the ^tli 

 are, according to Dr. Beale, distinctly demonstrated by 

 the ^jjth ; he observes, " I feel sure that further careful 

 study, by the aid of these high powers, of the develop- 

 ment and increase of some of the lowest organisms, and 

 the movements which have been seen to occur in certain 

 forms of living matter (amoeba, white blood-corpuscles, 

 young epithelial cells, &e.), will lead to most valuable 

 results, bearing upon the much debated question of vital 

 actions. 



" The most delicate constituent of the nerve-fibres of 

 the plexus in the summit of the papilla (see Phil. 2 J rans 

 for 1864) can be readily traced by the aid of this power. 

 The finest nerve-fibres thus rendered visible, are so thin, 

 that in a drawing they would be represented by fine 

 single lines. Near the summit of the papilla there is a 

 very intricate interlacement of nerve-fibres, which, although 

 scarcely brought out by the ^g-th, is very clearly demon- 

 strated by this power. In this object, the separation of 

 the fibres, as they ramify in various places, one behind 

 anothei > is remarkable, and the flat appearance of tbe 

 specimen as seen by the aVth gives place to that of con- 

 siderable depth of tissue and perspective. Tbe finest 

 nerve-fibres, ramifying in the cornea of the eye, and in 

 certain forms of connective tissue, are beautifully brought 

 out ; and their relation to the delicate processes from the 

 connective-tissue corpuscles can be more satisfactorily 

 demonstrated than by the ^th. The advantage of the 

 g\jth in such investigations seems mainly due to its re- 

 markable power of penetration." 



The one great drawback to the use of this objective, 

 and a very serious one to most microscopists, is its costli- 

 ness. The price of this power alone is almost more than 

 many can afford to give for a complete instrument. 



In flatness of field, and in perfection of definition, both 

 at the centre and margin of the field of view, few objec- 

 tives have equalled the recent T Vth of Mr. Eoss, who 

 appears to have inherited his late lather's Avell-known skill 



