ENZYMES. 75 
depended upon to keep the solutions free from bacteria. ‘This has been the case 
very frequently, and in several places in Greene’s interesting book on Fermentations, 
published in 1899, it is said or inferred that the addition of chloroform will prevent 
the growth of bacteria. This might or might not be true; much would depend 
on the kind of organisms present. The medium to which chloroform or thymol 
has been added must be shut in and shaken continuously if the full antiseptic value 
of these substances is to be obtained. 
THERMAL RELATIONS. 
The student should determine— 
(1) Maximum temperature for growth (thermostat). 
(2) Minimum temperature for growth (ice-box). 
(3) Optimum temperature for growth (room or thermostat). 
(4) Thermal death-point (ten minutes exposure in the water-bath, in thin- 
walled test-tubes of resistant glass having a diameter of 16 to 17 mm., ordinarily in 
10 cc. of moderately alkaline peptonized beef-bouillon, viz,-+15 of Fuller’s scale), 
(5) The effect of freezing (exposure to liquid air or to pounded ice mixed with 
coarse salt). 
Thermal relations are among the most interesting and should be studied with 
great care in case of every organism. They offer valuable means of differentiation 
and also very useful suggestions as to geographical distribution and habitat. Good 
thermostats are made by various people. Several items of construction are important. 
The water or oil jacket should be of considerable volume (thickness) so as not to 
change temperature quickly; the cover should be thick and of the best non- 
conducting substances. The opening for the thermo-regulator should be at least 14 
inches in diameter (so as to take a Roux metal-bar thermo-regulator) ; the warm 
chamber should be of good size; the space beneath should be high enough between 
floors to accommodate any pattern of safety burner; and last, but not least, the 
workmanship should be of the very best quality, so that the apparatus will not 
leak. Nearly every worker has probably had experience with leaky thermostats at 
some time in his life and knows what a vexation of spirit they cause, particularly 
if filled with oil. A very excellent kind of thermostat is the old, large-pattern, felt- 
covered instrument devised by Dr. Hermann Rohrbeck and figured in the lower 
right-hand corner of plate 8. This plate shows a thermostat room with four thermo- 
stats in use. All are provided with Roux metal-bar thermo-regulators and Koch 
safety burners. One is for quick shifts as needed ; and others are generally kept at 
30°, 37%4°, and 40° or 43° C. These temperatures, in conjunction with the cool 
boxes, thermal baths, and various room temperatures, enable one to quickly determine 
the thermal relations of an organism. ‘The height of the room is 10 feet, its depth 
7 feet, and its breadth 5 feet 3 inches. A larger room would be more convenient. 
Such a room should be located and constructed so as to be as little subject as 
possible to external changes of temperature. It should be lined with asbestos and 
sheet iron, and efficient safety burners should be used to the exclusion of all others 
(see Lautenschlager’s catalogue). The improved Koch safety burner is probably the 
best. All burners require frequent inspection. 
