94 PHOTO-MICROGRAPHS. 
seen in the photo-micrograph, but which, neverthe- 
less, is proved by experiment to be identical with 
it. If a little saliva containing these various or- 
ganisms be injected beneath the skin of a rabbit, 
the animal dies within two or three days, and 
its blood is found to contain vast numbers of the 
micrococcus seen in Fig. 2, Plate II* We have 
thus, by the expedient of introducing a fluid con- 
taining a variety of bacterial organisms into the 
body of a living animal, obtained a “pure cul- 
ture’ of a single organism, evidently because the 
conditions were favorable for the multipheation of this 
one, and not for that of the others. 
Upon the same principle, we may obtain a pure 
culture if a drop of fluid containing different 
micro-organisms is added to a “culture-fluid” 
suited to the development of one only; or to a 
fluid maintained at a temperature which is favor- 
able for one species and not for the others. 
In the case under consideration, a minute quan- 
tity of blood from the veins of a rabbit just dead, 
as the result of the experimental inoculation 
referred to, was spread upon a thin glass cover 
and allowed to dry. It was then stained with a 
weak solution of iodine (iodine, grs. ili, potassic 
iodide, grs. v, distilled water, grs. 200). The peculi- 
arity of this micrococcus, as it exists in the blood 
of a rabbit, is that it is surrounded by an aureole 
of transparent material which it is difficult to see 
in unstained preparations, because the refractive 
1 See paper by the writer in “ Studies from the Biological Labora- 
tory,” l. c. p. 184. 
