animal. Nuclein, itself, which is the substance nearest to the
beginning of a new cell, contains as high as ten per cent. of the
element phosphorus.

"On the other hand, phosphorus is the most limited of all the plant
food elements, measured by supply and demand and circulation.

"What is phosphoric acid? Well, the professor of chemistry says it
is a compound containing three atoms of hydrogen, one of phosphorus,
and four of oxygen. It is a syrupy liquid and one of the strongest
mineral acids. In concentrated form it is as caustic as oil of
vitriol. Why, here you have a Century dictionary. That should tell
what phosphoric acid is. This is what the Century says:

"'It is a colorless, odorless syrup, with an intensely sour taste.
It is tribasic, forming three distinct classes of metallic salts.
The three atoms of hydrogen may in like manner be replaced by
alcohol radicles, forming acid and neutral ethers. Phosphoric acid
is used in medicine as a tonic.'

"That," continued Percy, "is the complete definition as given by the
Century dictionary as to what phosphoric acid is, and I note that
this is the latest edition of the Century, copyrighted in 1902."

"We bought it less than a month ago," said Mrs. Thornton. "We can
have so few books that we thought the Century would be a pretty good
library in itself; Mr. Thornton has had too little time to use it
much as yet."

"Well, even if I had used it," said Mr. Thornton, "you see there are