( 850 ) 
culture-drop can have no harmful consequences; after the above 
mentioned investigations of CLARK and DuaGar caution is however 
advisable. 
Taking everything into consideration among the changes which 
NIEUWENHUIS proposes in my method, there is only one with which 
(and then only partly) I am in agreement and which is also in- 
corporated in my simplified apparatus (of which I had wished, for 
certain reasons, to postpone the publication): the two needle holders 
are replaced by one. When however he advises always the use of 
not more than one needle in isolating, we differ entirely. If he had 
carried out more extensive investigations with difficult material, for 
instance, with bacteria, instead of with the much larger fungus 
spores, he would not have suggested any alteration. 
I should be glad if the fact that the needles can now be obtained 
commercially, should lead to a more extensive use of my method. 
I am convinced that it has a large sphere of usefulness. Those who 
from the detailed description in my last publication conclude that 
the method is too difficult, are mistaken: I have thought it preferable 
to go into a minute description in order to make it as easy as 
possible for those who use it, however tempting it was to give the 
impression of a too great simplicity by a cursory description. 
For the rest, those who hesitate to isolate bacteria, can work 
with yeast or moulds. 
The technique of the method will improve by extensive use, for 
I cannot imagine it to be perfect. 
With regard to the alterations, proposed by Nimuwenuuis, I felt 
obliged to say at once, that in my opinion, they are not improvements. 
Finally one hint more: I advise those who can afford it to 
procure the apparatus with a moveable stand, on which the micro- 
scope is placed; although it seems to be more complicated it is the 
more convenient in use. 
Mathematics. — “On the integrating of series term-by-term”. Com- 
municated by Mr. J. C. Krurver. 
(Communicated in the meeting of January 28, 1911). 
When the function /'(r) is developed in a series converging 
uniformly for a<a«<b, we can integrate term-by-term, i.e., out of 
the equation 
aD 
F (z) = = vole) 
Uv 
follows 
