. TEXT-BOOK OF BACTERIOLOGY. 55 



still makes his sections with the razor instead of the microtome is 

 like the man who travels by coach when he could travel by train. 



In cutting- the sections both knife and preparation must be con- 

 tinually wet with alcohol, and the sections must be at once returned 

 into alcohol from the blade. They are then ready for staining-. 



Pour into a glass dish one of the diluted aqueous anilin coloring- 

 solutions and lay a section in it. It makes an important difference 

 whether the section is carried from water or from alcohol into the 

 staining fluid. In most cases the former proceeding- is preferable. 

 The diffusion processes, which play an important part in staining, 

 then operate more mildly, the tissue is less strongly penetrated by 

 the coloring matter, and consequently the after-process of bleach- 

 ing can be effected with more simple agents. 



When the section has remained from 5 to 15 minutes in the fluid, 

 according to the nature of the preparation and the coloring matter 

 employed, it must be placed in diluted acetic acid, in which the su- 

 perfluous stain is washed out. The acid is next removed by a short 

 exposure in distilled water, in which it must also be examined to 

 form a rough estimate of the success of the staining process. With 

 some practice and a careful glance it can immediately be seen 

 whether the staining is successful or faulty, and if it be the latter 

 case, whether the staining or bleaching was too strong, whether the 

 staining solutions were at fault, etc., etc. ' With a second section 

 endeavor to remedy the defects noticed in the first, and if this 

 proves satisfactory, proceed to submit it to further preparation. 



The next step is to render the tissue transparent, in order to 

 enable us to distinguish its component parts and to recognize its 

 finest details. This is done by the aid of ethereal oils and similar 

 means. Those most commonly employed are oil of cloves and oil 

 of cedar; the former of which, however, has the disadvantage that 

 it attacks and removes the stain, while the latter, on account of its 

 extreme sensitiveness to water, must be employed with particular 

 care. Oil of cloves can only bear small traces of water without 

 causing opaque cloudy specks on the preparation, and our aim must 

 therefore be to free the sections as completely as possible from the 

 water before placing them in the oil. 



This may be accomplished by placing them for a short time in 

 absolute alcohol after they leave the bleaching solution. 



The entire process, if it be desired to produce a typical nucleus 

 and bacteria staining on Weigert's plan, is as follows: The sec- 

 tions pass from distilled water into the staining 1 solution, thence 

 into a weak aqueous solution of acetic acid to bleach them, then 

 into distilled water to remove the acid then into absolute alcohol 



