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 Animals and Plants'' (Mikroscopische Untersuchungeniiber 

 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." 



