JO METHODS OF CULTIVATION OF BACTERIA. 



the screws being just tight enough to keep the parts in position, 

 and sterilise in the steam steriUser. Screw up more firmly so 

 as to make the rubber bulge slightly. Fill a hypodermic syringe 

 with some sterile glucose bouillon, push the needle through the 

 rubber d, and, tilting the point of the needle against the glass c, 

 slowly inject enough to form a drop on the under surface of c. 

 Withdraw the syringe and inoculate its point with the bacterium, 

 again introduce and inoculate the drop. Pass hydrogen through 

 one of the tubes for fifteen minutes, close the ends of the tubes, 

 and incubate at the required temperature. The apparatus can 

 be put on the stage of a microscope and examined from time 

 to time. 



Hanging-block Cultures. — Applying the principle of the 

 hanging-drop culture to solid media, Hill has introduced a new 

 method for the more accurate study of the morphology and 

 development of bacteria, which is equally applicable to aerobic 

 or anaerobic forms. Ordinary plain agar is melted down and 

 poured into a Petri's dish to the depth of one-quarter of an inch 

 and solidified ; a piece is then cut out of it about one-quarter or 

 one-third of an inch square and affixed to a sterile slide. The 

 upper surface of this block is then inoculated with a bouillon 

 culture of the selected organism in the manner of making a 

 cover-slip preparation, and the whole is covered with a small 

 sterile dish and set in the thermostat to dry for five or ten 

 minutes. This step being completed, a sterile cover-slip is 

 placed upon the inoculated surface, avoiding as far as possible 

 the imprisonment of air-bubbles, and cemented down with 

 melted agar by means of a platinum loop. The cover-slip with 

 the agar block is now to be removed from the slide and sealed 

 to a moist chamber with paraffin ; the preparation can now be 

 studied at room temperature, or transferred to a warm stage. 

 For the observation of anaerobes an alkaline solution of pyro- 

 gallol may be introduced into the moist chamber, which is then 

 made air-tight. 



Thermal Death-point Test. — It is sometimes necessary to 

 determine the death-point of a bacterium by exposure to moist 

 heat. This is most accurately performed by the aid of Stern- 

 berg's glass bulbs made in the fashion shown in Fig. 36. A 

 twenty-four-hour-old broth culture of the given bacterium, pre- 

 pared beforehand, is to be poured out into a sterile Petri's dish. 



