Balls —Temperature and' Growth . 
565 
second syphon with a clip serves to carry off the waste water from the 
bath. 
The other couple is also varnished thoroughly to avoid any galvanic 
effect, and is stretched across the moist chamber below the cover-slip, 
its ends passing out into the medium and air through the cement with 
which the cover-slip is fixed. A second plain, thin wire, which lies by 
the side of this couple, will be referred to later. The ends of the couple 
are rolled into springs and led through the air to the two unoccupied cups 
in the head of the paraffin sheet ; to permit of this the microscope is placed 
close to the right-hand side of the bath. This grouping of the cups 
automatically prevents any error which might otherwise arise in the circuit 
from subsidiary thermoelectric effects, since the remaining connexions of 
the switch and galvanometer are paired. 
Two of the like terminals of the couples are connected through the 
cups by a short piece of No. % o B. W. G. insulated copper wire, while 
similar silk-covered wires lead to the galvanometer, with a Du Bois 
Raymond key in circuit. 
The galvanometer is an Ayrton-Mather pattern D’Arsonval, made by 
the Cambridge Scientific Instrument Company, who are also the makers of 
the copper-constantin couples. 
The galvanometer scale is graduated continuously (in millimetres) in 
order to avoid possible errors in the transcription of plus and minus signs ; 
the zero is adjusted (at 30 cm. usually) by moving the scale, if necessary, 
before each experiment. The deflexion given for a difference in tem- 
perature of one degree Centigrade between the couples is about 60 milli- 
metres, as the instrument was set up in this work, so that errors are not 
likely to be made in the measurement of temperature. In practice the 
readings are made to the nearest half-centimetre, because the accuracy with 
which the bath thermometer can be read is considerably less than this ; an 
accuracy of c-i° C. is all that is aimed at, while even this is less than the 
errors which are likely to arise in the measurement of slowly growing 
hyphae. 
Culture Media. For general purposes the following formula has been 
used : — 
Peptone . 
Liebig’s Extract 
Pure Cane Sugar 
. . 2% Potassium hydrogen phosphate . 0.05% 
. . 0.5% Magnesium sulphate . . . 0-05% 
. . 0.5% Tricalcium phosphate . . . 0.01% 
Distilled water . . 97% 
When an exact knowledge of the chemical composition of the original 
medium was required, the Liebig and peptone were replaced by 1 per cent, 
of Urea. It may be pointed out for future study that the fungus seemed 
to find difficulty in growing on this medium at low temperatures (20° C.), 
but flourished at 3 A C. 
