185 
stance, capable of producing serious effects when they are eaten 
too freely and continuously. These injurious effects are oftenest 
seen in stock animals, but are not unknown in man. So serious 
were they during the sixteenth century that Germany and some 
other countries actually passed laws forbidding the use of peas 
and beans. 
Two methods are open to us for combating these injurious 
effects. The first is by so treating the foods in question that the 
harmful constituents are actually removed in preparing them for 
use, as is done in the fermentation of cassava and of the bitter 
yams already referred to. A very notable instance of this is the 
method just introduced in Germany for the utilization of the 
nutritive constituents of the common horse chestnut by the 
removal of its poisonous constituent. 
The second method, and much the better one, is the improve-~ 
ment of natural products by selection and cultivation so as to get 
them into the habit of ceasing to manufacture their peculiar poi- 
sons, as has been done with many of those named above. This 
subject is probably the most interesting of all those touched upon 
in the present lecture. Most of our cultivated foods are related 
to violently poisonous, but otherwise very similar natural products 
and some of them appear to have descended directly from the 
latter. Thus the melons, pumpkins, squashes and cucumbers 
are related with the poisonous colocynth, Elaterium and Luffa. 
The sweet potato is closely related to jalap, turpeth and similar 
tuberous roots, the yam to various deadly species of Dzoscorea, 
the asparagus and onion to squill and hellebore, the potato and 
tomato to belladonna and henbane. 
This shows us then two specific directions in which cultivation 
may greatly improve those foods in ae use or supply us with 
new foods derived from natural plant products not now fit for 
use; first by increasing their palatibility ie digestibility, second 
by eradually freeing them from objectionable or injurious con- 
stituents, Doubtless it is not too much to say, as I have once 
before remarked on this platform, that if we could know that one 
or two centuries hence all the sources of vegetable foods now 
grown upon were to be totally lost to us we should be able in the 
