Contagious or Epizootic Abortion in (!ows. 91 
considerably above that of the body. At the boiling temperature 
it becomes liquid, and it “ sets ” again when the temperature 
falls. It is obvious that if one mixes up a large number of 
abortion bacilli with such liquefied medium in a test tube and 
then allows the medium to become solid again, the different 
bacilli will be imprisoned at so many different points in the 
transparent substance, just as minute particles might be 
embedded in calf’s-foot jelly. The individual bacilli are, of 
course, quite invisible to the naked eye, but when they multiply 
each discloses its position by building up a visible speck of 
growth, just as a spore of common mould does when it grows 
on a piece of bread. Many different species of bacteria can be 
grown in this way, and as a rule when they do the specks of 
growth, or “ colonies,” as they are called, develop more .or less 
regularly throughout the whole of the medium. Generally, 
Fig. 1.— Abortion bacilli (magnification 2,000). 
however, the growths of abortion bacillus obtained in this 
medium have the appearance shown in the annexed figure 
(Fig. 2), from which it will be seen that the spots or colonies do 
not develop everywhere, but are confined to a definite narrow 
stratum which lies a short distance beneath the surface. The 
result is remarkable in view of the fact that what may be 
called the “ seed bacilli ” were scattered throughout the whole 
of the medium. Apparently the conditions favourable for 
their multiplication are present only at a slight distance from 
the surface, a fact which was interpreted by Bang as indicating 
that oxygen in the full strength in which it occurs in the 
