Nature and Cause of the Potato Disease. 
323 
current of elaborated sap extends not beyond the stolons, and yet 
the botritis is found below them ; and it is found, too, only in the 
medulla, the chief reservoir of the upward flow. 
9. Chemical Changes induced by the Disease. 
The changes induced by disease are, according to chemical 
analysis, clearly referable to putrefaction. But chemical analysis 
not only shows the disease to be that of putrefaction by the loss of 
azotised matter, but it supplies further evidence that the disease 
is a disease of the organs and not of the products — from the cir- 
cumstance that the organs -are the reservoirs of azotised matter, 
and it is azolised matter that suffers the greatest loss. 
I now present the results of two analyses made by myself, and 
which closely agree Avith those made by Dr. Playfair upon similar 
specimens : — 
Sound Tiibor. 
Diseased Tuber 
75-21 
. 78-61 
Starch . • . . • 
15-92 . 
16-01 
0-67 . 
• None. 
Colouring matter, flavouring and Hesin 
• • . 
1-02 
0-62 
Gum ..... 
1-25 . 
M7 
Albumen and Gluten . . , 
2 34 . 
0-32 
Ligneous fibre . . ... 
1-24 . 
1-02 
Silica, Alumina, Lime, Potash, Magnesia 
1, Phogjjhoricj 
2-35 
2-15 
and Sulphuric acids, and Chlorine 
100-00 . 
. 99-90 
The variations presented by these analyses in the constituents 
of the sound and diseased tuber are, that the diseased tuber con- 
tained 3*4 per cent, more water than the sound one ; the starch 
may be considered the same, as the difference is trifling • the 
colouring, &c., is somewhat lessened and the sugar gone; the gum 
is unchanged, the albumen and gluten nearly destroyed, accom- 
panied with a slight loss in the fibre. 
The inorganic constituents agree, if the excess of water in the 
diseased tuber be considered in the calculation. The most sig- 
nificant change that takes place in the constituents of the tuber is 
that of the disappearance of the albumen and gluten. These 
substances contain azote or nitrogen, and azotised bodies are prone 
to change when placed in favourable circumstances. A sound 
potato contains a free acid, and reddens blue litmus paper when 
applied to it ; but when the disease has set in, ammonia is gene- 
rated by the decomposition of albumen and gluten, and the 
potato becomes alkaline. Now, am.monia contains hydrogen and 
nitrogen in the proportion of 3 equivalents of the former to 1 of 
the latter; and hydrogen and oxygen form water; and water, 
carbon, and nitrogen form albumen and gluten. Hence the 
decomposition of the azotised matter furnishes ammonia as well as 
