ZOOLOGY AND BOTANY, MICROSCOPY, ETC. 



291 



object is placed on a cover-glass, which is cemented with vaseline to the 

 lower side of A, closing the opening. The space between the two rings 

 is filled with water. Two tubes at D admit air or gas to the interior, 

 and the top of the outer ring is closed at E by a cover-glass cemented 

 on. It is claimed that it combines the advantages 

 of the moist chambers of Bottcher and Eanvier. 

 The nutrient fluid has a free surface, as in 

 Bottcher's, but faces upwards instead of down- 

 wards, an advantage in many cases ; and, as in 

 Banvier's, is steady. It resembles Banvier's in 

 having the water, which assists in preventing the 

 evaporation of the nutrient fluid, separated from it. 

 The construction allows, moreover, of a new fluid 

 being introduced, and parts of the old one re- 

 moved, without, at least in certain conditions, 

 disturbing the vegetation. It is possible, there- 

 fore, to commence the culture with a single cell, 

 and proceed gradually to a large mass. The 

 chamber can be used only with Microscopes where 

 the objective is below, and the illuminating mirror 

 above the object which is being examined. 



Dr. T. JR. Lewis's Moist Slide * is shown in 

 fig. 54. Two semicircles of asphalt varnish were 

 brushed on the slide, one being rather larger than 

 the other, so that the ends of one half-circle 

 might overlap the other, but not so closely as not 

 to permit the entrance and exit of air. When nearly dry a minute 

 quantity of growing fluid was placed in the centre, upon which a few 

 spores were sown, a cover-glass being placed over 

 it, which adhered to the semi-dried varnish. The 

 slide was placed under a bell-glass, kept damp by 

 being lined with moist blotting-paper. 



Dr. Maddox's Slide is shown in fig. 55. A 

 strip of tinfoil is cut into two U-shaped pieces, 

 one being larger than the other, so that when the 

 smaller is placed upside down fl it will fi fc loosely 

 inside the upright portion of the other. These 

 are fixed in this position on a glass slide with a 

 little varnish, over which a thin cover-glass is so 

 arranged that the only air or foreign matter 

 which can reach the preparation must pass up 

 the " chimney " thus formed, between the inner 

 margin of the larger strip of the tinfoil, and the 

 outer one of the smaller. The arrows indicate the 

 spaces left open for the admission of air. 



Bertrand's Refractometer-t— Mr. E. Mallard finds that this instru- 

 ment X requires certain corrections due to the fact that the lower surface of 

 the hemispherical lens does not pass exactly through the axis of rotation. 



* 'Keport on the Microscopic Objects found in Cholera Evacuations, &c.,' 1870, 



t Bulf Soc. Franc. Mineral., ix. (1886) pp. 167-71. Cf. Neues Jahrb. f. 

 Mineral., i. (1888) Ref. p. 10. t See this Journal, 1887, p. 469. 



Fig. 55. 



