light from which the chemically active rays of ultra violet have 
been eliminated off. For this purpose the well known glass 
bulb is used; in this case it is not filled with ammoniacal copper 
oxide but with a not too dark solution of potassium dichromate (1 
gram suffices for a globe of 3.5 litres). If one wishes somewhat to 
soften the yellow light, which according to some is harmful, to the 
eyes, this can be done by placing a thin cobalt blue glass on the 
iris-diaphragm. 
Other important improvements are conneeted with the use of the 
moist chamber on which the coverslip is placed after the actual 
isolation has been accomplished. 
On consulting the handbooks on the method of making the so- 
called drop-cultures in moist chambers, one gets in general the impression 
that such cultures must invariably succeed. For years I knew no 
better, and attributed the miscarriage of many of the cultures I made 
to faults in my method of work, until I found in Kiisrer’s “Kultur 
der Mikroorganismen” on p. 54 the statement that all kinds of factors 
may here operate unfavourably. And when with reference to the 
papers quoted there, I read among others the broadly conceived and 
carefully executed experiments of CLARK and of Duccar 5), I saw that 
they had had the same experience as myself. CLark comes to the 
conclusion that some micro-organisms are sensitive even to slight 
differences in the concentration of the culture-drop, or to the vapour 
pressure inside the moist chamber. On the floor of the latter he places 
no drops of water but some drops of the same fluid in which the 
culture is grown. Then the vapour-pressure of the culture-drop and 
of the drops on the floor will be the same, and therefore there can 
be no reason for the culture-drop taking up or giving off water 
vapour, by means of which the concentration is altered. Since the 
rise of temperature in the closed space ef the moist chamber is also 
detrimental, Crark did not at once wholly close it with the cover-slip 
on placing it in the incubator, but left a small slit, which was 
afterwards closed. Further CLARK used relatively large moist chambers, 
for instance, a glass cylinder of 17'/, mm. in external diameter and 
10.7 mm. in height. Attention should be paid to these suggestions, 
as far as is possible, and also the cleaning of the cover-slip on which 
the investigators above-mentioned lay special stress is not to be 
1) J. F. Crark, On the toxic effect of deleterious agents on the germination and 
development of certain filamentous Fungi. Bot. Gazette 1899. vol. 28. p. 289. 
B. M. Duaaar, Physiological studies with reference to the germination of certain 
fungus spores. Bot. Gazette. 1901. vol. 31 p. 38. 
2) Liew p. 294. 
