GENERAL METHODS OF INVESTIGATION, BY S. STRICKER. V 



scopes, or the lower powers of compound microscopes, can 

 only be used with transmitted light, when general views of 

 the topographical relations of the tissues to one another are 

 desired. The larger the object, the lower must be the mag- 

 nifying power employed, in order that a general view of it may 

 be obtained. With such large objects it is usual to examine 

 them in the first instance with a low power, and then to 

 investigate the details of each part with a higher power. 

 The very powerful lenses lately manufactured by Hartnack 

 are extremely well adapted for the investigation of the living 

 tissues, or of the well preserved and isolated elements of 

 the tissues. In specimens which have been roughly treated 

 and are consequently not in a very fit state for microscopic 

 research, as in those that have been hardened with reagents, or 



dned with colouring matters, and repeatedly washed, very 

 tigh powers are in the first instance less instructive than 

 Lower ones ; indeed, those who are not very expert in the 

 of the instrument can actually see less with a No. 15 

 lan with a No. 8 Hartnack. However, the highest powers 

 re even here very serviceable to the beginner, if he be engaged 



the definition of the deeper lying tissues. It is only requisite 

 to use the fine adjustment with extraordinary care, to turn 

 the screw with great gentleness; so that a fresh field is 

 obtained, which may remain for some time under observation 

 prior to passing to a greater depth, or returning to a more 

 superficial part. 



But if well isolated and well preserved morphological ele- 

 ments are under observation, and if the tissues are examined 

 whilst still fresh, and without the addition of any fluids, or 

 only of those which occasion no change in them, the highest 

 powers prove of the utmost value. The advances that have 

 been made in our knowledge of cells and of the finer struc- 

 ture of nerve fibres are the result of researches undertaken with 

 the admirable instruments that have recently been constructed. 

 The value of these high powers is strikingly illustrated by 

 the investigations on the living cornea, conducted by Reckling- 

 hausen and Kuhne. It is indeed true, that in the perfectly 

 fresh state the structure of the cornea cannot be satisfac- 



)rily ascertained, even with the Lest glasses. In this state 



