LABORATORY RESEARCH, ETC. 267 
The tubes, which have two reservoirs -and two 
tapered ends (Figs. 105, 106), are very numerous in 
Pasteur’s laboratory. They are ranged on a stand in 
the way shown in the figure. 
It is ascertained that the contents of the tubes are 
really sterilized by leaving them for several days in 
a stove which is maintained at a temperature of 35°. 
In addition to the culture liquids already indi- 
cated, many others consist of various solutions of 
phosphates of lime and potassium, albuminous solu- 
tions, etc. 
Solid Nutritive Substances.—In order to isolate the 
different species of bacteria, and to obtain pure cul- 
tures, solid substances are now preferred : eggs, slices 
of potatoes and carrots, but especially gelatine and 
gelose—which ‘comes from Japan ready for use, and is 
said to be extracted from a marine alga—and the gela- 
tinized serum of the blood of oxen. All these sub- 
stances are transparent, so that the cultures can be 
easily observed in glass tubes. Koch, in his Berlin 
laboratory, makes almost exclusive use of solid media, 
which are first sterilized by similar precautions. 
In order to obtain pure cultures, all kinds of germs 
are first allowed to grow; then a very small amount 
of them is taken from the culture medium, and 
transferred to the sterilized medium, in which fewer 
microbes naturally appear. After several repetitions 
of this transplantation, sufficiently pure cultures may 
generally be obtained within a short time. 
