LECTURE ON BACTERIOLOGY. 
369 
utmost care having been taken to avoid contamination of onr 
virus (by heating the inoculating needle red-hot just before using), 
a puncture is made through the skin and a few drops of pure cul¬ 
ture injected into the loose areolar tissue of the neck. 
“ The wound generally closes on the second day. The in¬ 
guinal and axillary lymphatics become swollen on the eighth 
day. From this time the animals lose weight rapidly, and die in 
four or live weeks from the time of inoculation. In the spleen 
and liver the characteristic tubercular changes are found.” 
Koch’s results led him to believe that “ the bacilli occurring in 
tuberculous substances were not merely the attendants of tuber¬ 
culous processes but, the cause of them, and that the bacilli actu¬ 
ally represented the true tubercle-virus .” 
I have spoken thus of the tubercle-bacilli in order to give you 
a general notion of the processes employed, and the precautions 
necessary in this work. The steps are nearly the same with the 
bacteria found in other diseases. The same extraordinary pre¬ 
cautions are always necessary to avoid contamination. Some 
thrive in one fluid, some in other, some at ordinary temperatures, 
some at the body-heat. 
From my remarks thus far you may have inferred that it is a 
very easy matter to find the bacterium of any particular disease, 
but I must correct this error. Let us place a particle from the 
discharges of a cholera patient uuder the microscope. Among 
the objects filling the field are numerous little curved rods—the 
comma bacilli. But if you now substitute a drop of fresh normal 
saliva for the choleraic discharge, you will find little curved rods 
in every respect like the commas of cholera. I may as well say 
at once that the microscope alone will not enable us to determine 
whether a given bacterium is pathogenic or not. You have 
already seen that each species possess peculiarities of growth in 
our culture tubes. 
Bacteria also frequently afford peculiar chemical reactions. 
For example, nitric acid will discharge the color from all bacilli, 
artificially dyed with anilin. except those of tubercle and anthrax. 
One species is stained readily with one dye, that leaves another 
unaltered. Thus we are enabled in the laboratory to determine 
