ENZYMES. 75 



depended upon to keep the solutions free from bacteria. This has been the case 

 very frequently, and iu 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 i ^ 

 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^, 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. 



