422 
POPULAE SCIENCE EEVIEW. 
in some of the peripheral organs of vertebrate and invertebrate 
animals_, very fine fibres can be followed as they lie upon 
different planes, and their precise relation to other tissues 
oan be accurately determined. 
The most delicate constituent nerve-fibres of the plexus in 
the summit of the papillae of the frog^s tongue (New Obser- 
vations upon the Minute Anatomy of the Papillge of the Frog^s 
Tongue, Phil. Trans, 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 twenty-fifth, is very clearly 
demonstrated by the fiftieth. In this object the definition of 
the fibres, as they ramify in various planes one behind another, 
is remarkable ; and the fiat appearance of the specimen, as 
.seen by the twenty-fifth, gives place to that of considerable 
depth of tissue and perspective. The finest nerve-fibres 
ramifying in the cornea and in certain forms of connective 
tissue are beautifully brought out by this power, and their 
relation to the delicate processes from the connective-tissue 
corpuscles can be more satisfactorily demonstrated than with 
the twenty-fifth. The advantage of the fiftieth in such inves- 
tigations seems mainly due to its remarkable power of 
penetration. 
It should be stated that the specimens of animal tissues 
which I have subjected to examination by very high powers 
are mounted in strong syrup, or in the strongest glycerine, 
according to the process detailed in How to work with the 
Microscope,^'’ 3rd edition, p. 204. It is perfectly true that no 
advantage results from examining by the aid of very high 
powers the tissues of man and the higher animals immersed 
in water, or in fluids of which water is the chief constituent ; 
nor is it possible to make the specimen suflGlciently thin for 
examination with very high powers if immersed in a limpid 
fluid. The arrangement of the nerve-fibres I have referred to 
is not to be demonstrated in tissues immersed in water. The 
finer branches of the nerves are, in fact, quite invisible until 
the specimen is well impregnated with a highly refracting 
fluid. The imperfect methods of preparation usually employed 
for examining the higher tissues have given rise to a prejudice 
•against the employment of high powers. It cannot be too 
strongly insisted upon that very high powers are useless to 
those who have not had considerable practical experience in 
preparing specimens, and too much thought and care cannot 
be bestowed upon the process of preparation which the 
observer has determined to adopt. 
