ETIOLOGY OF TUBERCULOSIS. 
61 
periment. Of several covering glasses, provided with a dried on section, let the 
first not be heated at all, the second drawn once through the flame, the third 
twice, etc. When after this the covering glasses are treated with color solutions, 
it appears that the coloring of the cell grains and bacteria shows no difference 
between the one not heated at all and those drawn through the flame from one 
to four times. Also the forms remain unchanged. If the heating is carried far¬ 
ther and the covering glasses oftener drawn through the flame, the bacteria 
gradually lose the power of taking the coloring material, while the cell grains 
become colored even after very intense heating. In the covering glasses which 
have not been heated the section separates itself more or less, often entirely, also 
the dissolving “ eiweisskorper ” (white-of-egg bodies) form with the coloring 
matter precipitates, which cover the section and make the recognition of bacteria 
very difficult and even impossible. Better results are given by the covering 
glasses which have been once or twice drawn through the flame, but those drawn 
through three times give the best. One of these last the section clings uniformly, 
the “eiweisskorper” are insoluble or so nearly so that no more precipitates are 
formed, also the bacteria and cell grains take the color, with an even degree of 
intensity, while the surrounding substance remains wholly or almost. wholly un¬ 
colored. On this account I always proceed thus: After the sections spread out 
on the covering glasses have become completely dry, which always takes place in 
a few minutes, I draw them three times with moderate quickness through a Bunsen 
burner. The color-solution is placed in a watch glass or a flat vessel, and after the 
heating the covering glass is laid face downward on the liquid, that it swims. 
One must be careful that there are no air bubbles under the glass, as otherwise 
the section would not be wet in these places and therefore not colored. Then 
let the color-solution be so far heated that it just begins to bubble, and after 
once boiling leave the coloring glass upon it about ten minutes; the result will be 
a sufficiently powerful coloring. Better results are nevertheless reached when 
the covering glass swims for several hours on the unheated solution. In all diffi¬ 
cult cases, when one wishes to prove the existence of single bacilli, it is well to 
leave the covering glass twelve hours or longer in the color-solution. 
When one wishes to examine sections of tissues with reference to tuberculous 
bacilli,* pieces of the organ in question, not too large, are to be well hardened in 
absolute alcohol. Other hardening processes make difficult or even hinder the 
coloring of the bacilli. The sections need not be very thin, because by means of 
the double coloring, single bacilli can be distinguished very easily even in quite 
thick sections. Nevertheless, it is more to the purpose to prepare large sections, 
since the distribution of the bacilli is often very irregular, therefore it is possible 
that in small sections no bacilli may be found. The use of the microtome in the 
preparation of the sections is for this reason almost invaluable. The sections are 
immediately laid into the color-solution and remain in the same at least twelve 
hours. They can remain in it several days without injury. 
The sections as well as the layer clinging to the covering glass have, when 
taken out of the color-solution after the given time, a dark blue, almost black-blue 
color. In this condition all parts of the tissue are almost evenly dark colored, 
and it is scarcely possible to recognize the coarser structures. In order to make 
the preparation suitable for microscopic investigation, a great part of the coloring 
