PATHOLOGICAL HISTOLOGY. 
175 
to the searching and coloration of microbs, and it is indeed ap¬ 
plicable not only to the demonstration of the epidermis, but also 
to the parasites of the liver, the kidneys and the muscular and 
other tissues. This proof is based upon the use of eosine as color¬ 
ing matter, and then to the potash solution to clarify the prepa¬ 
ration and bring out the parasites. Potash has for a long time 
been recommended for the discovery of parasitic cutaneous af¬ 
fections. Employed alone, it gives excellent preparations, but 
lacking in the quality of permanence. On the contrary, when 
eosine lias first acted upon the isolated fragments of epidermis or 
upon hairs, or sections of the tissues to be examined, the potash 
acts effectually in fixing the coloring matter upon the parasites 
by clearing up the surrounding parts. As the action of acetic 
acid upon carmine fixes it in the nuclei of cells, so does that of 
potash fix the eosine upon those of spores and myceliums. 
This is, therefore, more like a modification of the whole pro¬ 
cess, than a new one. It is, however, so simple and so rapid that 
we have felt constrained to publish_it for the public advantage. 
The modus jaciendi is this : 
After freeing the segment or fragment to be examined of oily 
or greasy particles, by treatment with oether or alcohol, it is placed 
in a saturated alcoholic solution of eosine, where it is suffered to 
remain for a length of time, which varies according to the bulk 
of the object. From half an hour to an hour is generally suf¬ 
ficient ; aeliorion is colored in a few minutes. The excess of 
eosine is then washed with distilled water. This is an indispens¬ 
able precaution, as in the solution of potash, the free eosine forms 
lumpy masses which interfere with the clear appearance of the 
preparation. Instead of distilled water, it may be better to use 
the solution of potash. At last the fragment to be examined is 
left in the potash solution, 40 per 100, and protected with a glass 
cover. During the succeeding days, any loss by evaporation is 
replaced by the addition of one or two drops of the solution. 
After a few days, and sometimes even after a few hours, the 
preparation is sufficiently clear and the eosine sufficiently fixed 
upon the parasites. The solution of potash evaporated is then 
replaced by a saturated solution of acetate of potash, introduced 
only at the edges of the glass cover, which is to be surrounded 
