.ETIOLOGY OF TUBERCULOSIS. 
65 
vince himself of the necessity of the optic helps here described as absolutely 
necessary, if one first examines a properly colored section in water and examines 
it microscopically by a dry system or a water-immersion system and a compara¬ 
tively narrow “blendi” (blind or opening). Fine distinctions of color, and 
small colored bacteria in tissues, which are to any extent rich in grains, can under 
these conditions scarcely be distinguished. Also placing the section in glycerine 
changes almost nothing, because the differences in refraction of the parts of the 
tissue are equalized much too slowly and insufficiently. A noticeable improve¬ 
ment is gained by brightening the preparation by means of highly refractive 
liquids, such as oil of cloves, oil of cedar, etc.; for the brightening rests upon the 
more or less thorough destruction of the structure-image. But even this improve¬ 
ment is not sufficient to allow the color-pictures to appear in full clearness and 
sharpness. Only the quantity of light pouring in from all sides by means of 
Abbe’s illuminating apparatus and the oil-system can fulfill this task. Who only 
cares to examine covering-glass preparations, without caring for complete cer¬ 
tainty with regard to the state of things, for him a microscope with water- 
immersion system and without illuminating apparatus, will in case of need prove 
itself sufficient. Dry systems are not to be used for bacteria investigations. As 
soon as reliable investigations of finer bacteria are to be undertaken, or if one 
wishes to gain an independent judgment as to the newer results of bacteria re¬ 
search, it is absolutely necessary to have at hand the very best optic helps, that 
is to say oil-immersion systems and Abbe’s illuminating apparatus. With regard 
to the magnifying powers which must be used for the examination of tubercu¬ 
lous bacilli, I will remark that 500-700 fold magnifying power is most to the 
purpose, and that this is best reached with an oil system of an inch and the 
corresponding oculars. 
In the practical use of the coloring processes just described, the component 
parts of the tissue of the body conduct themselves almost without exception dif¬ 
ferently from the tuberculous bacilli. While the latter, in spite of the treatment 
with nitric acid, alcohol and vesuvian, keeps the dark blue color which they have 
taken, the remaining animal tissues, as already mentioned, lose the blue color again, 
and in the second coloring the grains of the cells as well as the products of destruc¬ 
tion of the latter, further the little grains of the plasma-cells are dyed brown. 
Only some parts of the tissue make an exception, as hair and epidermis, 
which remain more or less blue-colored. Since in these last tuberculous bacilli 
are hardly to be sought for, the finding of bacilli in the tissues is made exceedingly 
easy, by their characteristic conduct towards aniline coloring matters. Even in 
the closest masses of grains and in the midst of broken down cells, which often 
take all possible forms, from the smallest little points and micrococci like forms, 
to the longish staff-like forms, one can with absolute certainty distinguish 
single tuberculous bacilli from these closely similar forms by means of 
their dark blue color, which in the brown-colored surrounding and owing 
to the light-absorbing power of the brown ground appear as staffs almost 
colored black'. This noticeable difference in the color-reaction holds nevertheless, 
as must constantly be repeated, only for the method of coloring described 
here. A different preparation of the objects than the quick and good al¬ 
cohol hardening of the organs, made the condition here, appears to bring about 
