188 TECHNOLOGY OF BACTERIA. 



saturated* solution of acetate of potash, or a weak 

 solution of carbolic acid (one per cent), or camphor 

 water, may be used for this purpose. The surplus 

 fluid is removed with blotting paper, and another 

 circle of cement is turned about the margin of the 

 cover to hermetically seal the cell. Permanent 

 preparations may also be made by mounting in 

 Canada balsam. In this case, the cover-glass is 

 allowed to dry after staining, and may be treated 

 with alcohol and oil of cloves, although this is 

 usually unnecessary ; and too long an exposure to 

 the action of these agents is likely to remove the 

 color from the bacteria. 



To demonstrate the presence of bacteria in the 

 tissues, the following method, devised by Weigert, 

 is strongly recommended by Koch : 



" The objects for examination are first hardened in 

 alcohol. The sections made from these are allowed to 

 lie for a considerable time in a pretty strong watery 

 solution of methyl- violet. They are then treated with 

 dilute acetic acid, the water removed by alcohol, cleared 

 up in oil of cloves, and mounted in Canada balsam. . . . 



" This is of course only a general outline of the 

 method ; for the individual tissues, and more especially 

 the different forms of bacteria, show so great a variety 

 of result from such treatment that it would be impos- 

 sible to lay down rules which would be universal and 

 which would apply to every case. For many objects 

 fuchsin is best adapted ; for others the methyl colors 

 are more suitable. Among these latter there exists 

 such a difference in the staining power that the sec- 

 tions must lie in one solution only a few minutes, in 

 another several hours. . . 



