504 



SUMMARY OF CURRENT RESEARCHES RELATING TO 



Fig, 91. 



gained by using an alum solution instead of water. The objective is 

 shown at A, the coarse and fine adjustments at B and C, the clamp 

 for the objects M, the stage diaphragms at D, and a second dia- 

 phragm at the back of the condensers at B e. The latter is actuated 

 by the screw E in fig. 88. 



With objects which must remain horizontal, the contrivance 

 shown in fig. 90 is used, with smaller condensers L and a shorter cone 



E, the rays being deflected by 

 Fig. 90. „^-^ two prisms P and P', above 



and below the stage and ob- 

 jective (0). It is only suit- 

 able for low powers, and has 

 been used more especially for 

 showing living chicken em- 

 bryos. 



A second subsidiary appa- 

 ratus or "Sciopticon" (fig. 91) 

 is used for small amplifica- 

 tions of very large objects, 

 such as large brain sections. 

 The water vessel E in front 

 of the condensers L is rect- 

 angular, and the objective O 

 is composed of photographic lenses. Ah extensible camera B is 

 interposed between the object and the objective, and the focal ad- 

 justments are made either by compressing or extending the camera, 

 or by moving the objective alone by the milled head T. At 4^ m. 

 distance from the screen amplifications of 18 to 25 times are 

 obtained. 



A table is given showing the amplifications, with the various 

 objectives, from 370 to 8000; the highest powers used being 

 Seibert's Nos. VIII. and X. water-immersion (3800 and 8000 respec- 

 tively). 



As a screen for the reception of the images, a plate made of the 

 finest gypsum, 1*5 m. in diameter, is used, placed 4*5 m. from the 

 objective. Upon this a human red blood-corpuscle appears, with a 

 Seibert X objective, as a disc of 6 cm. in diameter. The amoeboid 

 movements of white blood-corpuscles are perfectly visible to a class 

 of 300 persons (the more distant ones provided with opera-glasses). 

 In order to make the white blood-corpuscles quite distinct, Professor 

 Strieker passes through the fresh blood a solution of fuchsin in 

 water, containing • 6 per cent, of common salt. The living cells 

 absorb the pigment very slowly, whereas the fluid in which they are 

 contained takes a distinct red colour. The white blood-corpuscles, 

 therefore, appear as bright, white spots on a coloured ground, and do 

 not lose anything of their mobility. 



In preparing sections for use with an electric Microscope they 

 require to be somewhat deeply stained, and stains should be chosen 

 which show the histological elements in strongly contrasted colours, 

 such as carmine, gold, or silver staining. 



