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R. ItOCFT. 
free from bacteria germs by heating them at least an hour at 150-160° C. in a double 
walled heatingbox made of sheet iron. One fills the re-agent glasses about one-third 
with serum, and closesthem immediately with a stopper made of cottou wadding. 
In spite of all this care there are regularly found in the blood serum bacteria germs, 
which come from the air, from the hair of the slaughtered animal, etc., and would 
very soon cause decay and decomposition of the serum if they were not destroyed. 
Other liquids destined for the “reincultur” of bacteria can be sterilized, that is 
made free from all bacteria germs, easily and certainly by boiling. This cannot 
be done in the case of blood serum, because by higher temperature it completely 
loses its transparency. There remains, therefore, only the method adopted by 
Tyndall in the sterilization of hay-infusion, that is, instead of heating it once to 
a boiling temperature, to heat it repeatedly at a temperature of 55°-60°. The 
bacteria, namely, if not spore-bearing, are easily killed in liquids even by a tem¬ 
perature of 55°. The spores, on the contrary, as is well known, endure these 
temperatures and do not die until the boiling point is reached. Once heating of 
the liquid, therefore, only kills the spore-free bacteria and leaves the spores which 
may be there untouched. In the medium so favorable to their growth, however, 
the spores germinate soon, changing themselves into bacilli, and as such cannot 
stand a temperature of 55° they are therefore killed by successive warmings before 
they have had time to form new spores. But since the spores germinate at differ¬ 
ent times, and often do not develop into bacilli until after several days, it is neces¬ 
sary to repeat the warming. Experience has taught that it is almost always suf¬ 
ficient to warm the blood serum for an hour for five successive days to free it 
completely from germs which are capable of development. This warming can 
take place in an open water bath. It is safer to use a tin vessel especially kept 
for the purpose and which possesses double walls filled with water and a cover 
constructed in the same manner, so that the warming shall be equal on all sides. 
The blood serum sterilized in this manner is then stiffened, and in order to 
get the greatest possible surface for inoculation the re-agent glasses should be held 
in a very slanting position. Also tin boxes with a double bottom and a glass cover, 
placed in a slanting position, are practical for this purpose. The water in the 
bottom of the glass is so heated that a thermometer lying in the box between the 
re-agent glasses shows 65° C. In this temperature the serum stiffens in from half 
an hour to an hour. The serum of different animals is not uniform in its conduct. 
The serum of sheep usually stiffens most quickly, calf serum most slowly. When 
serum is warmed at a higher temperature, for example at 70°, it stiffens far more 
quickly, but it is then more difficult to keep it transparent. A well-prepared blood 
serum must be almost completely clear, transparent and amber-like. At most 
only at the lower end of the re-agent glass and in the thickest layer may it be 
whiter and less transparent. It must also not be too soft, but must almost have 
the consistence of a hard-boiled hen’s egg. 
During the warming, usually on the upper cooler wall of the re-agent glass, 
more or less steam condenses and forms drops which, when the re-agent glass is 
taken up flow down and collect between the deepest part of the serum and of the 
glass wall. A small part of the area of inoculation is covered by this liquid. Never¬ 
theless the liquid is in so far of value that it takes up by diffusion soluble sub¬ 
stances from the stiffened blood serum and is changed into a very good breeding 
