320 THE MICROSCOPICAL NEWS. 
tinguished. By this system of testing, one drop of water from the 
Spree has been found to contain 1000 germs, which filtration seems 
unable to remove. In testing earth, it can be strewed over a glass 
plate on which gelatine has previously be placed. The value of 
these processes will, it is considered, be much appreciated in testing 
the action and value of various disinfectants. —Lance?. 
PRACTICAL PROCESSES IN VEGETABLE 
HISTOLOGY 
By L. OLIVER, in Rev. Sci. Nat., 1882. 
Taken from the Journal of the Royal Microscopical Society. 
N studying the structure of a living organism it is not sufficient 
to examine under the Microscope the form and relations of 
its elements. We must, in addition, determine the chemical 
nature of each. In this physiology is as much concerned as 
general anatomy, physiological functions being the resultant not 
merely of the molecular composition, but also of the arrangement 
of the organic structures. 
The endeavour has, therefore, been to find for histology reagents 
capable of discovering in the interior of the cells the presence of 
the analysed substances. 
Two methods have been adopted. The older and more general 
consists in examining, under the Microscope, different preparations 
of the same organ, before and after the successive action of certain 
agents on it. Note is taken of what this complex treatment elimi- 
nates, precipitates, or colours. This result is compared with that 
obtained by a different treatment of the same organ, or by the 
similar treatment of a different organ, thence deducing the 
characters of the tissues experimented on. Thus pieces of wood, 
in which the Microscope reveals the existence of cells, vessels, and 
fibres, no longer show cells after being subjected to the influence 
of certain substances. Another series of reagents causes them to 
lose their fibres without destroying their vessels, whilst the former 
resist the treatment which dissolves the walls of the vessels. 
It is to this kind of analysis that we have been so long limited. 
The increasing perfection of practical microscopy now enables us 
to substitute for it a more certain and productive method, that of 
micro-chemical reactions. 
* Rey. Sci. Nat., i. (1882) pp. 436-54 ; ii. (1882) pp. 71-91. 
