160 



PURE CULTURES FROM PATHOLOGIC MATERIAL 



the case it is practically impossible to keep an incubator stationary. 

 When a stationary temperature is of the utmost importance, as, for 

 instance, in the preparation of attenuated cultures to be used as 

 vaccines (anthrax vaccine), the gas cannot be used as it comes from 

 the pipe, but must first be led into a gas-pressure regulator and from 

 there to the thermoregulatoi . Electric thermoregulators for use 

 in connection with gas lamps have also been constructed. The author 

 has not yet had much experience with the electrical thermostat, where 

 electricity furnishes the source of heat, and he does not know whether 

 these are more reliable than the incubators heated by gas. Incubators 

 are, of course, not all regulated to a temperature of 37 C.; they are 

 frequently set for 22 C., and for special purposes at other temper- 

 atures. 



FIG. 84 



FIG. 85 



Reichel bacteriologic filter: a, receptacle; 

 b, porcelain filter; c, arm for vacuum pump; 

 d, outlet. 



Pasteur culture filter. 



Bacteria Filters. In order to separate soluble toxins from the bac- 

 teria which have produced them in fluid culture media, it is necessary 

 to filter the latter. Even the best and densest filter papers would 

 not do for this purpose, since bacteria can pass through the pores. 

 Pasteur, Chamberland, Berkefeld, and others have devised filter 

 masses which are so dense that bacteria cannot pass through them. 

 Kaolin, clay, and other similar substances, moulded into the form 

 of bougies, cylinders, or flasks, are the masses used. They are not 

 glazed, of course, because this would make them impervious to a 

 watery fluid. Such filters vary in the size of their pores, and those 

 having the smallest will not permit even the most minute micro- 

 organisms to pass. The Pasteur-Chamberland filter generally has 

 smaller pores than the Berkefeld filter. Whenever a fluid medium 

 in which bacteria have been grown is filtered for the purpose of obtain- 



