4 
difficulty, if at all, digested in the stomach. These walls may 
thus be left intact until the a is reached, being there 
digested off and the contents expose the ee processes 
in that organ. Some of these contents may, however, be much 
better adapted to stomach digestion than to intestinal digestion, 
t they cannot now avail themselves of such preference. 
It must be remembered further that it is only the best quality 
of vegetable foods whose cell-walls consist of pure or nearly pure 
cellulose. The great majority of plant tissues have their cell 
walls mets in various ways, the usual result being that theic 
digestion becomes much more difficult. Thus, the cells of wood 
tissue, onecully of pure cellulose, become lignified by the addi- 
tion to their walls of a thick coating of almost indigestible lignin. 
The cells of cork are invested with suberin, almost impervious to 
the digestive juices. The term ‘‘cork,’” as here used, include 
all substances of the same nature as that composing the tissue of 
ordinary corks, such substances, or very similar ones, being 
exceedingly abundant in vegetable foods 
e facts are of the utmost importance for our consideration 
in this lecture. They prove conclusively that the human diges- 
tive organs cannot deal so effectively or generally with vegetable 
as with animal foods, and they prove with equal certainty that 
the problems of selecting vegetable foods and of preparing them 
for our digestive organs, are much more serious and difficult than 
are those relating to animal foods. It is these considerations 
which must occupy us in our attention to the lectures which will 
follow in this course. They will receive special attention in our 
eighth lecture, by Miss Shapleigh, on the selection and prepara- 
tion of vegetable foods. 
In this connection, it must be remembered that great numbers 
of highly nutritive vegetable products are unavailable as foods 
because of the presence in them, along with their nutrients, of 
poisonous constituents of one sort or another. Some of these 
eliminated by cultivation and plant breeding that those sub- 
stances have now become staple and valuable foods. The lima 
