30 MICRO-ORGANISMS AND DISEASE. [CHAP. 



of an animal dead of anthrax into a drop of nourishing material, 

 fluid or solid, on the centre of a clean cover-glass, the edges of 

 which have been prepared as just mentioned, and fasten this 

 on the above slide so that the specimen faces the concave pit : 

 expose this so prepared specimen to a constant temperature, 

 either by placing it in the incubator and examining it with the 

 microscope from hour to hour, or on the warm stage (Strieker, 

 Ranvier) used in histological work for directly observing the 

 influence of temperature on the various cells and tissues ; or, 

 place it simply on the stage of the microscope and expose the 

 whole (i.e. microscope and all) in a suitable warm chamber 

 (after Klebs), but so that the chamber allows light to pass by 

 means of a small window to the mirror of the microscope, while 

 the eyepiece is so arranged as to project through a hole in the 



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Fia. 7. A GLASS CETA,, FOR OBSERVING TTNDER THE MICROSCOPE THU 

 PROGRESS OF GROWTH OF MICRO-ORGANISMS 



The upper figure shows the cell in perspective ; the lower figure in profile or 

 cross section. 



A. Glass slide. 



B. Cover-glass. 



C. Glass ring forming the wall of the chamber. 



P. Drop of nourishing material in which the micro-organisms grow. 



upper wall of the chamber. The plan which I generally follow 

 is with slight modifications that of Koch. 



A glass cell (Fig. 7) is made by cementing a glass ring, - 

 inch in diameter and about ^ T V inch high, on to an ordinary 

 glass slip. The chamber of this cell is well cleaned with 

 absolute alcohol. A thin cover-glass, square or round, about 

 one inch in breadth, is well heated by holding it for a few 

 .seconds over the flame of a gas-burner or spirit-lamp. On 

 the upper edge of the above glass ring is placed with a camels' 

 hair brush a thin layer of clean olive oil ; a droplet of water 

 is deposited on the bottom of the cell in order to keep this 



