ZOOLOGY AND BOTANY, MICROSCOPY, ETC. 



331 



then coarse ft ml fine gravel again. Each stratum is separated by a layer 

 of gauze. 



Boiling hot water is first run through the apparatus. It is then 

 placed in a steamer until the whole is heated to 100°, after which the 

 boiling-hot agar may be introduced. The apparatus acts very rapidly, 

 and turns out quite clear agar. 



Fig. 58. 



C3> 



Coarse Gravel 

 Fine O ravel 



New Method of Obtaining Pure Cultures.* — S. L. Schouten has 

 devised a delicate procedure for obtaining pure cultures of bacteria by 

 selecting an individual cell with the aid of the Microscope. An extremely 

 thin layer of vaselin is spread on a cover-glass. On the cover-glass 

 are placed a drop of very dilute culture and a drop of sterile nutrient 

 medium. The cover-glass is then placed in a moist chamber, which is 

 perforated on two sides. Through the apertures pass two small glass 

 hooklets, by means of which the culture drops in the chamber can be 

 manipulated. The chamber is then placed under the Microscope (oil- 

 immersion), when the culture-drop and the medium-drop will be seen 

 lying close together, and the water in the chamber as minute droplets on 

 the vaselin layer. The bacteria are sought for and isolated by means 

 of one of the hooklets, which are worked by micrometer screws. In this 

 way a single bacterium is fished out and deposited in one of the water- 

 droplets. When the operator is satisfied that there is only one bac- 

 terium, the microbe is transferred by means of the other glass booklet 

 to the drop of culture-medium. The glass needles are about 5 /i thick, 

 and the hooklets about 30 //, diameter. 



By this method the fission of a single bacterium, the formation of a 

 colony, and so on, can be observed, and the isolation effected in a liquid 

 medium, which is not possible by Koch's method. 



* Verslac;en van het Geneosk. Congree, 1899. See Centralbl. Bakt., l ,e Abt., xxix. 

 (1901) pp. 363-4. 



