280 



TECHNICAL MICROSCOPY. 



particular conditions (e.g., excluding the air, in a drop of liquid sur- 

 rounded by carbonic acid, hydrogen, or mercury), a moist chamber, 

 such as Geissler, of Berlin, prepares (Fig. 157 c, culture-cell), is 

 most convenient. It has a central space for 

 observation, which is connected at two 

 opposite points with inlet and outlet tubes, 

 The walls of the chamber in the centre are 

 of the thickness of a cover-glass, and are 

 flattened so closely together as to form a 

 capillary space. When filled with a liquid, 

 which is allowed to flow out again, a drop 

 will always remain in the middle capillary 

 ^ ^~ -^ space, which may be examined in its whole 

 ) p ^^ extent, even with high-power objectives. In 



C _Y |f C~\ -~ic khis shallow chamber, therefore, a fungus- 

 f^ \ j spore, yeast-cell, &c., may be placed with the 



proper nourishing fluid. Gases or liquids may 

 be introduced during the process of develop- 

 ment by means of an aspirator, which is con- 

 nected with the outlet tube of the chamber. 

 For the study of the processes of division 

 in the lower algre (spiro-gyra, &c.), which 

 usually take place at night, the method 

 applied by Strasburger 1 is to be recom- 

 mended, by which the division can be 

 delayed till the following day. The glasses 

 in which the algre are confined are placed in 

 a temperature of less than 5 C. By this 

 means the processes of division are interrupted, but they commence 

 again on the following morning in the normal temperature of the 

 room even with the brightest illumination. 



FIG. 157. 



III. 

 THE PEESERVATION OF MICROSCOPIC SPECIMENS. 



THE collection of microscopic objects, especially those which 



we obtain by a careful preparation, or by a fortunate chance, has 



in recent times owing to the improvement of our methods of 



1 Strasburger : " Zellbildung und Zelltheilung," p. 34. 



