2 BOTANICAL MICROTECHNIQUE. 



drop of fluid with a cover-glass in most cases greatly 

 hinders the access of oxygen. In such cases the so-called 

 moist-chamber is commonly used. This is closed above by 

 a cover-glass, from whose lower surface a drop of culture 

 fluid, containing the micro-organisms to be observed, hangs 

 free (observation in the hanging drop). 



Such a moist-chamber can be prepared most simply from 

 card-board about 2 mm. thick. A rectangular piece is cut 

 a from this, a little smaller 



than the glass slide to be 

 used, and a square open- 

 ing is then cut in its mid- 

 dle, with sides about 4 

 mm. shorter than the 

 cover-glass to be used 

 (cf. Fig. i, a). These 

 card-board cells are 

 thrown, before use, into 

 boiling water, by which 

 they are at the same 



FIG. i. Moist-chamber for the culture of micro- . 



organisms. time saturated and steril- 



ized. While still wet they are placed on slides, and then 

 the cover-glasses, with the organisms to be cultivated in 

 hanging drops on their under sides, are placed upon them. 

 The covers are so placed as to rest upon the card-board on 

 all sides, as is shown in Fig. I, b, which represents such a 

 moist-chamber in longitudinal section. 



The culture drop is thus freely in contact with a large 

 volume of air, and is protected from evaporation by keep- 

 ing the card-board wet by the occasional addition of a few 

 drops of water. 



Besides this, various other moist-chambers have been 

 used for the same purpose, as, for example, slides with 

 ground cavities, or glass blocks with hemispherical or lens- 

 shaped hollows. These offer, in some cases, certain advan- 

 tages ; but in general they are based on the same principle, 

 and their use is easily understood (cf. Strasburger, I, 415 

 ff., and Behrens, I, 51 and 162). 



