THE CELL THEORY 249 
ical, and, later, to the Paris Academy of Sciences; but it was 
not till 1839 that the fully illustrated account was published. 
This treatise with the cumbersome title, ‘‘ Microscopical 
Researches into the Accordance in the Structure and Growth 
of Animalsand Plants” (Mikrosco pische Untersuchungen tiber 
die Uebereinstimmung in der Structur und dem Wachsthum 
der Thiere und Pflanzen) takes rank as one of the great classics 
in biology. It fills 215 octavo pages, and is illustrated with 
four plates. 
“The purpose of his researches was to prove the identity 
of structure, as shown by their development, between animals 
and plants.” This is done by direct comparisons of the ele- 
mentary parts in the two kingdoms of organic nature. 
His writing in the ‘Microscopical Researches” is clear 
and philosophical, and is divided into three sections, in the 
first two of which he confines himself strictly to descriptions 
of observations, and in the third part of which he enters upon 
a philosophical discussion of the significance of the observa- 
tions. He comes to the conclusion that “the elementary 
parts of all tissues are formed of cells in an analogous, though 
very diversified manner, so that it may be asserted that there 
is one universal principle of development for the elementary 
parts of organisms, however different, and that this principle 
is the formation of cells.” 
It was in this treatise also that he made use of the term 
cell-theory, as follows: “The development of the proposition 
that there exists one general principle for the formation of all 
organic productions, and that this principle is the formation 
of cells, as well as the conclusions which may be drawn from 
this proposition, may be comprised under the term cell-theory, 
using it in its more extended signification, while, in a more 
limited sense, by the theory of cells we understand whatever 
may be inferred from this proposition with respect to the 
powers from which these phenomena result.” 
