626 A MANUAL OF BACTERIOLOGY 



respectively. An arrangement can be supplied to prevent 

 both doors being opened simultaneously. The Washington- 

 Lyons apparatus, or its modifications, is an elongated 

 cylindrical boiler with double walls, forming a jacket, and 

 a door at each end. The chamber is of sufficient size to 

 admit bedding, and is built into the partition wall between 

 two rooms, so that each door opens into a different room. 

 Into one of the rooms the infected articles are conveyed, 

 and are placed in the disinfector as lightly packed as 

 possible ; when disinfected they are removed by the 

 opposite door into the other room, thereby avoiding all 

 chance of reinfection. Steam at a pressure of about 20 Ib. 

 is admitted into the jacket and then passes to the inner 

 chamber, the object of the jacket being to warm the 

 chamber, and so prevent condensation. For the same 

 purpose hot air is sometimes injected beforehand to warm 

 the chamber and articles, and after the steam disinfection, 

 can again be injected for drying. The length of time re- 

 quired for disinfection does not exceed a half to one hour. 

 In Thresh's disinfector the steam is generated from a 

 saline solution (calcium chloride), which has a boiling- 

 point (105 C.) higher than that of water. 



The thermal death-point of a number of organisms in pure 

 culture has been determined by many investigators. Eyre suggests 

 the following as " standard conditions " for determining thermal 

 death-points : 



1. Length of " time exposure " to be ten minutes. 



2. Emulsion to be prepared from " optimum cultivation." 



3. The vehicle in which culture is suspended to be sterile salt 

 solution or sterile distilled water. 



4. Strength of emulsion to correspond to about 1 milligramme of 

 culture per cubic centimetre. 



5. Bulk of emulsion to be not less than 3 c.c. 



6. Emulsion to be contained in test-tube of 1-5 cm. diameter with 

 walls 1 mm. thick. 



7. Emulsion to be exposed to moist heat in a water-bath regulated 

 by a delicate and accurate thermo -regulator. 



