64 
Busk on Starch- Granules. 
microscope, and the object-glass (i or ^) brought to a focus^ 
close to the upper edge of the piece of thin glass. With a 
slender glass rod, a small drop of strong sulphuric acid is to be 
carefully placed immediately upon, or rather above the edge 
of the cover ; care being taken that it does not run over it. 
The acid of course quickly insinuates itself between the glasses, 
and its course may be traced by the rapid change in the 
appearance of the starch -granules with which it comes in con- 
tact. The course of the acid is to be followed by moving the 
object upwards, and when, from its diffusion, the re-agent 
begins to act more slowly, the peculiar changes in the starch- 
granules, now also less rapid, may be readily witnessed. 
These changes in potato-starch are thus described by M. 
Martin.* " First, the amylum grain sinks in, in that place, 
where, according to Fritsche, the kernel (nucleus) is situated. 
On the surface minute fissures appear, two of which almost 
regularly diverge towards the thicker end of the grain. The 
grain continues to be depressed inwards until a cavity is 
formed which is surrounded by an elevated ridge. In pro- 
portion as the grain swells up, this ridge increases in circum- 
ference and decreases in breadth, that is, continues to get 
flatter until fissures, mostly of a stellated form, appear in the 
hitherto, little altered thicker part of the grain. The process 
is not very rapidly developed, and it is very difficult for the 
eye to follow it. Suddenly something is torn off, the grain 
is extended lengthways, and in the next moment a wrinkled 
skin of a rounded, generally oval shape, lies on the glass. 
Middle sized and small grains exhibit this shape most dis- 
tinctly ; and they have usually only one longitudinal wrinkle, 
the upper and lower ends of which are pointed. The constant 
appearance of this wrinkle is important for the development 
of my theory. The appearance of this disc," he goes on to 
say, " demonstrates that it is perfectly flat, and has a slightly 
elevated edge which also becomes flat on pressure. The con- 
tour is rounded, but perfectly sharp. If the two glasses be 
violently moved from one side to the other whilst pressing 
the amylum, the disc is torn, and it is distinctly seen, especially 
in the blue-coloured ones, to consist of two layers, an upper 
and a lower one. Further examination shows that they are 
collapsed vesicular bodies, consisting of an extremely fine but 
strong and elastic membrane." 
" The primary form, therefore, of the amylum grain," ac- 
cording to M. Martin, " is a spherical or ovate vesicle. If 
this be considered as empty, and so contracted that one-half 
* L. c, p. 279. 
