404 THE HISTORY OF BIOLOGY 



knowledge of the structure of the electrical organs. All these works, val- 

 uable as they are, are nevertheless put in the shade by a short essay in the 

 Archiv fur Anatomic und Physiologic of the year 1861, entitled " Uber Muskel- 

 korferchen und was man cine Zellc zu nennen habe." Schultze has hereby laid the 

 foundations of the modern idea of the cell. "What is the most essential 

 thing in a cell?" he asks at the beginning of the essay. The old theory^ 

 which, as we have seen, Virchow still embraced, would answer: " A vesicle 

 surrounded by a membrane, with a nucleus and fluid contents." Schultze 

 refers to the embryonic cells and points out that these consist of a mass of 

 protoplasm with nucleus, but without any surrounding walls; the membrane 

 which had previously been supposed to surround these cells, and which cer- 

 tain investigators had brought out by chemical means, he proves to be an 

 artificial product. He further points out that only cells without any mem- 

 brane can multiply by division; those cells possessing a membrane which are 

 found in the animal kingdom thus lead a restricted and limited existence — 

 "They may be likened to an incapsulated infusorian or an imprisoned ani- 

 mal." Again, the substance that surrounds the nuclei in the different tissues 

 — muscular fibrillas, connective substance — is not, as has been declared, 

 a substance foreign to the cell, but a transformation of the protoplasm itself. 

 Accordingly, the protoplasm, in conjunction with the nucleus, is the basis 

 of all the life-manifestations of the cell, and the very name "protoplasm," 

 which had hitherto been used only by the botanists, is introduced as the 

 universal term for the fundamental substance in the cell. And in connexion 

 therewith this substance is characterized with reference to the conditions 

 obtaining in plants, in the lower and higher animals; it is maintained that 

 the cell-mass is by no means a fluid, but an element having a definite form, 

 a consistency which is different in different animal forms and different kinds 

 of cell; it is indissoluble in water and possesses, when it is free to do so, an 

 independent power of motion, which is characteristic for different cases. It 

 is sometimes possible also for a number of nuclei to be surrounded by a com- 

 mon protoplasm, which again can afterwards form cell-boundaries and thus 

 produce isolated cells. The actual word "cell" Schultze reserves for the vital 

 element represented by the nucleus and the protoplasm, and this meaning 

 has also been retained since, illogical though it is, seeing that the word 

 "cell" means a space ivith walls, whereas the living cell is characterized 

 by the fact that it lacks walls. 



Improvement of histological technics 

 This contribution made by Schultze laid the foundations on which cell re- 

 search has since been built, and this marks a new era in the science of cy- 

 tology. The aids to research that the students of the period just described 

 had at their disposal had been comparatively limited — microscopes of prim- 

 itive construction, with which cells and tissues were studied in their natural 



