Staining Bacteria in Tissues 157 



traction between the blades. Sufficient stain is allowed to 

 run from a pipet upon the smear to flood it, but not over- 

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

 which it is thoroughly washed oft' with water. If the speci- 

 men is prepared for temporary use, it can be dried and ex- 

 amined 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 examination after 

 mounting in Canada balsam. 



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 

 of difficulty, and the method employed must be modified 

 according to the particular kind of organism. The success 

 of the method will depend upon the good preservation of 

 the tissue to be studied. As bacteria disintegrate rapidly 

 in dead tissue, the specimen for examination should be 

 secured as fresh as possible, cut into small fragments, and 

 immersed in absolute alcohol from six to twenty-four hours, 

 to kill and fix the cells and bacteria. The blocks are then 

 removed from the absolute alcohol and kept in 80 to 90 per 

 cent, alcohol, which does not shrink the tissue. Solutions 



