MOIST-CHAMBER CULTURE. 279 



pended drop. For this purpose we will use the simplest possible 

 moist chamber to wit a small frame of pasteboard. Such a frame 

 is cut out of tolerably thick pasteboard, its inner aperture being 

 somewhat smaller than the size of the cover-glass we propose 

 to use, while its outer diameter does not exceed the width of the 

 object-slide. This frame is soaked in distilled water till it is 

 completely saturated, and then laid upon an object-slide. 1 On 

 the middle of a cover-glass, which has been sterilised in a flame, 

 is placed a drop, spread out very thin, of the culture fluid, into 

 which the object for investigation is transferred. The cover- glass 

 is turned rapidly upside down, with the drop hanging below, and 

 laid upon the pasteboard frame. If the observation is to be long 

 continued, a few drops of water are from time to time placed upon 

 the frame, so that it shall not become dry. If the observation is 

 interrupted, the preparation can be protected from evaporation in 

 a large moist chamber composed of a bell-jar standing on a large 

 plate, with its edges immersed in water on the plate. In order to 

 again find a definite spot in the preparation, it is well to cut a 

 cross on the stage by means of a sharp instrument, right and left 

 of the central aperture. Then, when the object-slide is in the 

 required position, similar crosses can be made upon it with one 



1 After and before using the pasteboard culture-cell it is desirable to place 

 it for a few minutes in boiling water, so as to kill any organisms which may 

 adhere to it, or the culture may be vitiated. This applies equally strongly to 

 other cultures. If cultures are to be at all prolonged the pasteboard cell is 

 preferably replaced by one made out of a glass ring. These glass rings, about 

 JUinch high, are cut from glass tubing of suitable diameter, and have their cut 

 surfaces flattened quite horizontally upon a whetstone ; and are then fixed upon 

 the object-slide with Canada-balsam. A drop of water is placed at the bottom 

 of the cell to keep the air saturated, and a cover-glass of suitable dimensions, 

 after preparation of the hanging drop, is fixed upon the glass cell by oil-drops 

 run round its edge. Glass rings of this kind can be purchased, ready cut and 

 smoothed. Such a glass cell can be converted into a gas -chamber, for the 

 purpose of testing the influence of various gases upon living organisms, by 

 having openings in it opposite to one another, in which small glass tubes can 

 be cemented or fused, and the gas then drawn through by an aspirator. An 

 admirable gas-chamber is that designed by Prof. Marshall Ward, and figured 

 in Phil. Trans., 1892, vol. B, p. 131. Object-slides bearing moist-chamber 

 cultures may be placed in a plaster of Paris case, made with a removable 

 plaster lid. This will serve as an admirable moist-chamber for the culture 

 of fungi and bacteria, which do not need light, since the moisture from its 

 damped walls, or a water reservoir at the bottom, is very uniformly distri- 

 buted, and no drops of water can fall from above upon the preparation. 

 These cases are very easily made, and of any desired size. [Eo.] 



