I4 NOTES ON MICRO-ORGANISMS. 
and there into other groups of organisms will perhaps be 
allowed me. 
It is hardly necessary to say that the microscope is the 
indispensable adjunct to this kind of work, and the lenses of 
the instrument cannot be too good. Expense in these last 
does not necessarily mean excellence, and it is astonishing 
what remarkably good definition may be obtained with 
low-priced eye-pieces and objectives of certain makers, chiefly 
German. Amongst English makers, I should like to mention 
Messrs. Swift and Son, several of whose microscopes I have 
seen with higher combinations ranging from 300-450 diameters 
of magnification, and their performance leaves little to be 
desired. (I have one on the table before me, which perhaps 
some would like to examine later.) 
Where expense is not a matter for consideration, the 
indulgence in objectives such as those of Messrs. Powell and 
Lealand is no doubt productive of a commensurate amount 
of satisfaction. For all ordinary purposes a magnification of 
3-400 diameters is adequate, but since Bacteria require very 
good definition, the glasses should be carefully selected. There 
is nothing more irritating than to see objects looming through 
the tube of the microscope with blurred outline and uncertain 
structure, causing the observer to first doubt his own powers 
of perception, next to clean every glass in the instrument, and 
finally to arrive at the conclusion that the defect is practically 
irremediable, and the only cure is to obtain other powers. 
As regards manipulation and cultivation of the commoner 
organisms, comparatively simple appliances will in most cases 
enable the experimenter to secure fair results. It is somewhat 
different with the organisms connected with disease or certain 
pathological conditions. To study these efficiently a more 
considerable array of apparatus is essential, and conveniences 
and opportunities requisite that are only enjoyed by the 
medical faculty and a few others. Time, patience, and 
reasonably good eyesight are other indispensables for work 
on micro-organisms, and a capacity for sketching is decidedly 
