Ellis,— The Life-history of Bacilhis hirtus . 
235 
It will be seen that the size of the spore can only be utilized for diagnostic 
purposes, when it approaches either the maximum or the minimum given 
in the above table. As the length of the spores of Bacillus hirtus is 1 -5-2*5 ^ 
and the breadth i-o-i -8^, they rank as very large spores, being surpassed 
in the above list only by Bacillus tumescens. 
With regard to the appearance of the spores, this can only be satis- 
factorily examined by staining, as without any treatment we see nothing 
except a very strongly refractive oval mass. Fig. 1 shows the spores 
treated with an Iodine stain. The intine is very clearly marked as a brown 
peripheral layer forming the boundary of the very strongly refractive 
contents. The exine, by this method of staining, is somewhat difficult to 
see, usually only a slight shimmer, radiating on all sides from the spore, is 
seen. By allowing the stain to act for a somewhat longer period, it 
becomes visible at last as a faint line surrounding the intine. The intine 
can be seen more clearly by slightly raising the tube above the focus-point. 
When the adjustment is very slightly below the focus-point, the whole 
spore is coloured uniformly brown. The best stains for this purpose are 
Methylene-blue or Fuchsin. Stained with Methylene-blue (1 c.c. alcoholic 
sat. solution of Methylene-blue to 40 c.c. H 2 0 ) the spores are more rapidly 
and more distinctly coloured, and it is not difficult to investigate the 
structure of the exine. It is seen to be a slightly irregular coat, which at 
both poles has a somewhat blunt point (Fig. 2). The intine is more 
distinct, and can be seen still more clearly by very slightly raising the tube 
above the focus. When the stain has acted for some time the spore 
becomes permeated throughout. In this condition the intine and its con- 
tents contract somewhat, probably due to the effect of the alcohol used in 
the making of the stain. This brings into prominence the structure of the 
exine, which does not take part in the contraction (Fig. 3). This stain is 
to be recommended as the best for this purpose. When stained with 
Fuchsin (2 c.c. sat. ale. solution, 10 c.c. abs. ale. 10 c.c. H 2 0 ), it was found that 
after about ten minutes, the exine was sharply brought into prominence. 
The intine, however, was only seen as a dark line, limiting the strongly 
refractive contents, but was not coloured. With this stain, as with 
Methylene-blue, the bluntly pointed ends of the exine are plainly visible 
(Fig. 4). In Fig. 5 is shown a spore much more highly magnified, which 
illustrates more clearly its structure when treated with reagents. The 
spore is thus seen to be an oval structure, with two coats, the inner, delicate 
and closely wrapped round the contents, the outer a looser somewhat 
irregular band, to the presence of which is due the resistance of the spore 
to heat and other injurious influences. When seen ‘ end on ’ the spore 
appears round (Fig. 6). In some cases, especially in unstained preparations 
that have not been dried on the coverslip, the spores are sometimes seen 
obliquely. In such cases the spore varies in shape between the circular and 
