TEXT-BOOK OF BACTERIOLOGY. 237 



the beginning has entered the blood-current and can be distributed 

 in it, a more extended miliary appearance of the tuberculosis, a 

 sudden inundation of the body by the micro-organism, is noticed at 

 once. 



We shall, therefore, generally have to deal with cases of the 

 nature first considered, and the pathologico-anatomical lesions will 

 be in conformity with it. 



The macroscopic picture differs greatly according to the ani- 

 mals infected. We may find an extensive necrosis without actual 

 cheesy degeneration (liver and spleen of Guinea-pigs), or rapid soft- 

 ening and formation of thin, liquid purulent secretion (tubercle of 

 monkeys), or simultaneous consolidation and cheesy deposits (mur- 

 rain of cattle), or formation of compact tumor masses with im- 

 bedded lime concrements (tuberculosis of the hen), etc. 



But these general apparent differences appear alike on micro- 

 scopic examination, and the histological structure is in all cases the 

 same. 



The distinguishing criterion for the existence of tubercular 

 changes is, of course, the presence of bacilli. It is, then, obvious that 

 we must properly prepare the tissues in order to prove the exist- 

 ence of these micro-organisms. 



The staining of sections is done essentially according to the 

 principles followed with the cover-glasses. First place the sections 

 in a little cup with carbol-fuchsin and let them remain for about 

 one hour. The duration of staining must be correspondingly longer, 

 because we must not, in this case, heat the fluid to accelerate the 

 process, for fear of destroying the sections. Next follows the decol- 

 oration in diluted nitric acid (10$), into which the sections are dipped 

 with a needle for about one-half to one minute, according to the 

 thickness of the preparation and intensity of the stain. 



The red color will change into a distinctly green or greenish-blue 

 tint. Seventy- per- cent alcohol will wash out the coloring matter 

 dissolved by the acid, and the fuchsin leaves the section slowly in 

 dense red clouds. This process having terminated and decolora- 

 tion accomplished, the sections will show only a rose-red shade, al- 

 most completely fading, especially in the thinner parts of the prep- 

 aration. The counter- stain ing is done, as with the cover-glasses, 

 with ordinary methyl-blue. The sections remain here about two 

 to three minutes, are decolored and deprived of water in absolute 

 alcohol, brought into the clarifying oil, spread on the slide, and, 

 finally, imbedded in Canada balsam. 



On examining such a preparation with a high magnifying power 

 the bacilli will be recognized as red rods on a blue background, 



