178 Methods of Observing Micro-organisms 



shown in the cut. This altogether prevents capillary at- 

 traction between the blades. When the material is spread 

 upon the slide no forceps are needed, and the method corre- 

 spondingly simplified. Sufficient stain is allowed to run 

 from a pipet upon the smear to flood it, but not overflow, 

 and is allowed to remain for a moment or two, after which it 

 is thoroughly washed off with water. The smear upon a 

 slide is then dried and examined at once, a drop of oil of 

 cedar being placed directly upon the smear, and no cover- 

 glass used. If the staining has been done upon a cover-glass, 

 it can be mounted upon a slide with a drop of water between, 

 and then examined, though this is less satisfactory than ex- 

 amination after mounting in Canada balsam. 



Fig. 34. Stewart's cover-glass forceps 



Sometimes the material to be examined is solid or too 

 thick to spread upon the glass conveniently. Under such 

 circumstances a drop of distilled water or bouillon can be 

 added and a minute portion of the material mixed in it and 

 spread upon the glass. 



When the bacteria are contained in urine or other non- 

 albuminous fluid, so that the heat used for fixing has nothing 

 to coagulate and fix the organisms to the glass, a drop of 

 Meyer's glycerin-albumen can be added with advantage, 

 though the precaution must be taken to see that this mix- 

 ture contains no bacteria to cause confusion with those 

 in the material to be studied. 



The entire process is, in brief: (i) Spread the material 

 upon the glass; (2) dry do not heat; (3) pass three 

 times through the flame; (4) stain one minute; (5) wash 

 thoroughly in water; (6) dry; (7) mount in Canada 

 balsam. 



To Observe Bacteria in Sections of Tissue. Har- 

 dening. It not infrequently happens that the bacteria to 

 be examined are scattered among or inclosed in the cells 

 of tissues. Their demonstration then becomes a matter 



