554 TEE POPULAR SCIENCE MONTHLY 



culties with which they had to contend. The microtome, the micro- 

 scope, and differential staining methods, in their present-day perfection 

 did not exist for them. It was the day of the razor and hand sectioning. 

 The first microtome appears to have been that iised by Professor His in 

 1866; the improvements leading to the perfection of the present-day 

 microtome did not begin until 1875. The development of the objective 

 of the compound microscope was just beginning in Schwann's time 

 (1830). Although iodine was early used, it was not until about 1857 

 that Geleach called attention to carmine, the first nuclear stain to be 

 introduced into histological technic. At first, tissues were examined 

 only in the fresh state and even later when hardened they were not 

 imbedded as now in celloidin or paraffin, but placed between vegetable 

 pith or blocks of amyloid organs during the process of cutting. 



Surely the technical difficulties were great and we are not surprised 

 that both Schleiden and Schwann believed new cells to be formed 

 through a process of " crystallization " from a " mother liquor " or 

 cytoblastema and that the cell was a vesicle with a solid wall. This 

 question of minute structure and that of mitosis yielded eventually to 

 improvements in teclinique and Schleiden's theory of the formation of 

 cells de novo was discarded, and we know from Yirchow's famous 

 aphorism " omnis cellula e cellula " that in his time it was established 

 that cells arose only by the division of preexisting cells. This general 

 law was the result largely of the work of botanists, as Hugo von Mohl 

 and Nageli, and was applied by Virchow (1858) to animal tissues only 

 after much work had been done on such tissues by Kolliker, Eeichert 

 and Eemak. It was not until 1873 (Anton Schneider) that an insight 

 into the details of cell division was gained and it was 1882 when the 

 part of the nucleus in karyokinesis was satisfactorily demonstrated and 

 Flemming could supplement Yirchow's aphorism with another " omnis 

 nucleus e nucleo." 



Thus did Schleiden, a botanist of the University of Jena, and 

 Schwann, assistant (1824r-1838) to Miiller, establish one of the most 

 brilliant and most important generalizations of the century, which 

 became at once the basis of all morphological studies, and, as applied 

 by Virchow, placed pathology on a scientific basis, and has continued 

 as a result of its general biological applications — to development, in- 

 heritance and immunity — to influence medicine profoundly. As Ver- 

 worn has said : 



It is to the cell that the study of every bodily function sooner or later 

 drives us. In the muscle lies the problem of the heart beat and that of muscular 

 contraction; in the gland cell resides the cause of secretion; in the epithelial 

 cell, in the white blood corpuscle, lies the problem of the absorption of the food, 

 and the secrets of the mind are hidden in the ganglion cell. 



It will be necessary to return to the cell theory again in discussing 



