5 66 
Balls . — Temperature and Growth . 
Solid media were made from these by the addition of 1-5 per cent, 
agar and 0*5 per cent, gelatine. 
Experimental Methods. 
Sterilization. After an experiment the chamber and beaker are washed 
and dried. Before the next experiment they are soaked in water at 
a temperature of 70° C. and rinsed with the culture medium. If these 
precautions are taken, bacteria rarely appear within the three hours which 
an experiment commonly occupies ; the experiment is disregarded for 
critical purposes if any are seen. 
Antiseptics cannot be employed on account of the difficulty of removing 
all traces of them from the wall and cement of the chamber. 
Preparation of the Culture . The plan finally adopted was to inoculate 
a test-tube which contained 30 cc. of the medium under examination with 
a very small piece of mycelium from the aerial hyphae of an old, cool- 
grown, agar tube. The test-tube was left overnight at a temperature of 
1 5° C. to 20 0 C. (unless some special temperature effect was under study) in 
order to allow new hyphae to develop. A disk would thus be formed of 
about 5 millimetres diameter. 
A fragment of mycelium would then be taken from the margin of this 
mycelial disk, and placed in the chamber for observation. The size of this 
fragment was kept as small as possible, less than a millimetre in diameter 
and with a probable dry weight of about *0001 grammes. 
By thus allowing the fungus to develop in the medium to be tested, 
we ensure that the new hyphae shall contain the same percentage of the 
excreted bodies (if any) in their cell-sap as was contained in the medium. 
Growth Measurement. The tiny fragment of fungus is clipped in 
position under the cover-glass by means of the thin wire which lies by the 
side of the chamber-couple. The chamber is then placed in the beaker and 
the latter is filled with the culture-medium from the test-tube ; the air 
imprisoned in the chamber is sucked out if necessary, and oxygen or other 
gas is passed in by the capillary tube ; the end of the latter is plugged with 
a glass rod. 
The beaker is then placed in the water-bath, which is filled with 
water of the desired initial temperature and placed on the stage. The 
ends of the chamber-couple are led to their mercury cups. 
The Zeiss D 1 objective dips into the excess of culture medium which, 
flowing over the surface of the cover-glass, protects it from the sudden 
changes of temperature formerly mentioned. The No. 4 Zeiss eye-piece 
contains a micrometer scale, one division of which is equal to -003 mm. 
with this combination of lenses. This unit of -003 mm. is the one employed 
in the curves transcribed at the end of this paper. Under favourable 
