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COLLOIDS IN BIOLOGY AND MEDICINE 



Though a skilled ultramicroscopist usually recognizes impurities from irregular 

 intensity of illumination and color of the submicrons, as well as by differences in 

 motion, the most extreme care is necessary in ultramicroscopic work. 



Cover glasses for the upper chamber should be of quartz, 3/4 mm. thick. 

 The usual methods of cleaning (cloths, brushes, elderpith and Japanese tissue) 

 are to be avoided, as particles, which may cause much trouble, are broken off; 

 scratches, tears, and impurities arising from dry cleaning increase the adsorption 

 of colloids on the chamber walls and reveal their own ultramicroscopic pictures 

 independently of the colloid particles. The chamber and cover slip must always 

 be cleaned in the following fashion: nothing is touched by hand, only forceps 

 with platinum points or with a loop of platinum wire about them may be used. 

 The apparatus is placed in a hot mixture of concentrated H 2 SO 4 and sodium bi- 

 chromate, then washed with tap water and finally conductivity water. The water 

 must be removed with ultra-alcohol and finally collodion is poured over the cleaned 

 surface. Before use, the collodion skin may be easily raised at one corner and 

 removed. 



On forcing the chamber and cover slip in the holder, it is necessary to avoid 

 screwing too tight or tensions will arise which gradually equalize themselves and 

 cause st nations which are very disturbing. 



Ultramicroscopes for the Study of Organized Material. 



The apparatus for this purpose may be adjusted to any microscope. 

 Special preparation of the objects is unnecessary. 



Objects difficult to make visible by staining or which are too small 

 to see alive with the ordinary microscope are especially suitable for 



FIG. 35. Abbe condenser with 

 central opacity. 



FIG. 36. Paraboloid condenser for the 

 dark-field illumination of organisms. 

 (From H. Siedentopf .) 



this method of investigation, e.g., spirilla, protoplasmic structures, 

 etc. A picture is obtained similar to that with BURRI'S India ink 

 method, in which the rest of the field is blackened with India ink, 

 while the objects appear bright. Oblique illumination reveals in- 

 homogeneities and structures which would be invisible even with 



