110 BIOLOGY AND TECHNIQUE 



The Staining of Bacteria in Tissues.^The preparation of tissue for 

 bacterial staining is, in general, the same as that employed for purposes 

 of cellular studies, in histology. For bacteriological studies the most 

 useful fixative is alcohol; other fixations, such as that by formalin, 

 Zenker's fluid, or Mueller's fluid, give less satisfaction. In other respects 

 the details of dehydration and embedding are the same as those used in 

 histological studies, except that it is desirable that the tissues should be 

 handled rather more carefully than is necessary for ordinary patholog- 

 ical work, and the changes from the weaker to the stronger alcohols 

 should be made less abruptly. 1 



Embedding in paraffin is preferable to celloidin, although the latter 

 method is not unsuccessful if carefully carried out. The chief disadvan- 

 tages of celloidin are the retention of color by the celloidin itself and the 

 consequent unclearness of differentiation. It is also easier to cut thin 

 sections from paraffin blocks than from those prepared with celloidin. 



When staining tissue sections for bacteria, it is most convenient 

 to carry out the process with the section attached to a slide. For cel- 

 loidin sections this may be accomplished by means of ether vapor. For 

 paraffin sections it is necessary to cover the slide with an extremely thin 

 layer of a filtered mixture of equal quantities of egg albumin and glycerin, 

 to which a small crystal of camphor or a drop or two of carbolic acid 

 has been added. The sections are then floated upon a slide so prepared, 

 and set away in the thermostat for four or five hours. 



LOEFFLER'S METHOD. 2 Stain in alcoholic methylene-blue solution 

 five to fifteen minutes, or in Loeffler's alkaline methylene-blue solution 

 one to twenty-four hours. 



Wash in one to one -thousand acetic acid solution for about ten 

 seconds. 



Treat with absolute alcohol by pouring the alcohol over the prepara- 

 tion for ten to twenty seconds. 



Clear with xylol. 



Mount in balsam. 



When celloidin sections are stained in this way ninety-five per cent 

 alcohol should be substituted for the absolute. A number of other 

 staining solutions may be used in the same way, aqueous fuchsin or 

 aqueous gentian-violet yielding good result. 



1 For details of such work reference should be had to the standard textbooks on 

 pathological technique, notably the very excellent one of Mallory and Wright. 



2 Loeffler, Mitt. a. d. kais. Gesundheitsamt, ii, 1884. 



