a. e be +-— uc MMNMREDLUL LT 
13 
frozen and thawed ; the cells forming the tissue are separated 
from each other and lose their cohesion, instead of being 
firmly agglutinated together as in their sound state ; and 
consequently the rasp is unable to tear the cells in pieces, 
but separates them from each other whole, without allowing 
the starch they contain to escape. A small number only of 
the cells are lacerated, and it is they which yield what starch 
the manufacturer obtains from them, a quantity which 
scarcely amounts to 3 per cent. The principal part of the 
starch remains locked up in the pulp which is thrown away. 
M. Payen was led incidentally to notice the different 
proportions of starch lodged in the different parts of a 
potatoe; and he found that the smallest quantity exists in 
the centre, which is separated by a circular row of fibres from 
the outer part, which is the true bark of the tuber. The 
latter, or cortical part, which abounds in starch, is divided 
from the epidermis by a thinner tissue, in which is almost 
exclusively deposited the acrid and venomous matter of the 
plant, and which is entirely without starch. 
This observation explained to M. Payen the cause of 
frozen potatoes being acrid and strong tasted. In their sound 
state the acrid matter contained in the rind of the potatoe is 
not mixed with the other fluids of the parenchyma of the 
tuber; but when frost has separated the cells of the paren- 
chyma, the fluid then extravasated flows into their interstices, 
and the acrid and venomous matter dissolved by them par- 
takes of the general diffusion; it is the physical effect of 
the tendency which fluids placed in contact have to mix with 
each other. 
Proceeding from these observations M. Payen has ex- 
amined in what manner frozen potatoes can be turned to 
some useful purpose. As they have not lost any part of their 
starch, they ought to preserve, after being thawed, all their 
alimentary qualities, if they are quickly dried after having 
been properly prepared. M. D'Orbigny states, that in Peru 
this mode of preserving potatoes for food is commonly em- 
ployed. The Peruvians cause the tubers to be frozen on 
their mountains, and then bring them down into their valleys, 
where the heat rapidly dries them; and in this state of desic- 
cation they preserve tlteir nutritive property for an indefinite 
time. 
It would therefore appear not only that potatoes when 
