CULTURE MEDIA. 



45 



The following method of filtering agar has recently (1890) been 

 proposed by Karlinsky. It is a modification of the method previously 

 described by Jakobi and depends upon the use of pressure. 



In Fig. 18, a is a cylindrical vessel of tin, which is closed above by 

 a perforated rubber cork, through which is passed a glass tube, b. 

 This is enclosed in a larger tin cylinder, c, which contains water, 

 which may be kept hot by placing an alcohol lamp under the pro- 

 jecting arm d. The central cylinder has a tube, e, passing through 

 the bottom of the hot-water cylinder, and which is provided with a 



Fio. 19. 



stopcock for drawing off the filtered solution. Before pouring the 

 hot agar solution into the cylinder a, a cotton filter about ten centi- 

 metres thick is placed at the bottom of this cylinder and hot water 

 is poured upon it while the stopcock of the outlet tube is open. This 

 washes out the cotton and prepares the filter for the agar solution. 

 The apparatus is supported upon a tripod, not shown in the figure. 

 Filtration is said to occur rapidly when the air in the central cylinder 

 is compressed by means of the hand bellows attached to the tube b. 

 Unna (1891) has devised a filtering apparatus for agar which is 

 shown in Fig. 19. In this the pressure of steam is utilized. A hollow 



