48 MICRO-ORGANISMS AND DISEASE. [CHAP. 



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 afterwards well supplied with moisture ; a drop of 

 the sterile nourishing material (broth, aqueous humour, 

 hydrocele fluid, blood- serum, liquefied gelatine mixture, 

 liquefied Agar-Agar mixture, &c.,) is then deposited by means 



FIG. 10. A GLASS CELL, FOR OBSERVING UNDER THE MICROSCOPE THE 

 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. 



of a capillary pipette on to the centre of the cover-glass ; 

 then the point of a capillary pipette or needle containing the 

 material it is desired to sow is rapidly plunged into the drop 

 of the nourishing material (or if this is solidified is deposited 

 in lines or points on the drop of nourishing material), the 

 cover-glass inverted and placed on to the glass ring : the 

 layer of olive oil keeps the edges of the cover-glass air-tight 

 on the glass ring. This cell is then placed into the incubator 



