[4] The discovery is also attributed to Hamm, a medical student, and to Hartsoeker, who claimed priority in the discovery.
[5] De Formatione Intestinorum, Nova Commentar, Ac. Sci. Petrop., St. Petersburg, XII., 1768; XIII., 1769.
[6] Besides biographical sketches by Stieda, Waldeyer, and others, we have a very entertaining autobiography of Von Baer, published in 1864, for private circulation, but afterward (1866) reprinted and placed on sale.
[7] It is of more than passing interest to remember that Pander and Von Baer were associated as friends and fellow-students, under Döllinger at Würzburg. It was partly through the influence of Von Baer that Pander came to study with Döllinger, and took up investigations on development. His ample private means made it possible for him to bear the expenses connected with the investigation, and to secure the services of a fine artist for making the illustrations. The result was a magnificently illustrated treatise. His unillustrated thesis in Latin (1817) is more commonly known, but the illustrated treatise in German is rarer. Von Baer did not take up his researches seriously until Pander's were published. It is significant of their continued harmonious relations that Von Baer's work is dedicated "An meinen Jugendfreund, Dr. Christian Pander."
THE CELL THEORY—SCHLEIDEN, SCHWANN, SCHULTZE
The recognition, in 1838, of the fact that all the various tissues of animals and plants are constructed on a similar plan was an important step in the rise of biology. It was progress along the line of microscopical observation. One can readily understand that the structural analysis of organisms could not be completed until their elementary parts had been discovered. When these units of structure were discovered they were called cells—from a misconception of their nature—and, although the misconception has long since been corrected, they still retain this historical but misleading name.
The doctrine that all tissues of animals and plants are composed of aggregations of these units, and the derivatives from the same, is known as the cell-theory. It is a generalization which unites all animals and plants on the broad plane of similitude of structure, and, when we consider it in the light of its consequences, it stands out as one of the great scientific achievements of the nineteenth century. There is little danger of overestimating the importance of this doctrine as tending to unify the knowledge of living organisms.