TlIK J'OSITION OF CYTOLOGY IN BIOLOGICAL SCIENCE 5 



ui)()ii the remarkable process of mitosis, the chromosomes occupying an 

 csijecially prominent place in researches of the period. Noteworthy 

 progress was also made in studies of the physiological processes occurring 

 in cells and the relation of these to the activities of the organism of which 

 they are parts. As examples may be mentioned the advances in knowl- 

 edge of mineral nutrition, enzymes, osmotic concentrations in cells, and 

 the permeability of the plasma membrane. 



The life cycles of various groups of plants and animals were minutely 

 described in terms of the multiplication and differentiation of cells. The 

 details of cell and nuclear behavior during the organism's reproductive 

 phases were examined with special care, for it was realized that two 

 successive generations of individuals are connected by a minute single 

 cell — in some cases a spore, in others a fertilized egg — and that this 

 single cell must therefore contain in its organization some kind of basis 

 for the type of organism developing from it. A discovery of cardinal 

 importance was that of the fusion of two nuclei, one from each parent, in 

 the process of fertilization (1875). 



It was observed further that certain organisms do not consist of cells 

 in the usual sense, but are extensive and continuous masses of cytoplasm 

 containing large numbers of nuclei. Notwithstanding this lack of internal 

 cell partitions or of fixed nuclear positions, these organisms develop 

 characteristic body forms and internal specializations. Moreover, 

 certain organisms mainly cellular in structure pass through a non- 

 cellular stage at some period in their development or possess certain 

 noncellular tissues in the mature body. 



Discoveries like the foregoing not onh" furnished partial solutions to 

 the problems originally attacked, Imt the}^ also made it possible to 

 formulate with the necessary precision those further special questions', 

 requiring answers before the problems in their broader aspects could be 

 regarded as solved. It is thus bit by bit, rather than by one stroke, that 

 an understanding of fundamental biological processes is reached. Even 

 now, a centur}^ after researches on the division of cells began, we have 

 arrived at no complete explanation of that remarkable process. 



Mention should be made of technical advances made during the 

 classic period. Far better methods for fixing and staining tissues were 

 devised. With the aim of preserving cells with a more nearly natural 

 appearance, careful studies were carried out on the effects of many rea- 

 gents upon the various parts of the protoplast. Other investigations 

 revealed the usefulness of coal-tar dyes which were then being produced 

 for the first time. Formerly onh'- a few natural dyes such as carmine and 

 hematoxjdin were employed, and although these are still extremely 

 valuable today, the coal-tar dj^es have added greatly to the variety and 

 effectiveness of staining procedures. Vastly improved section-cutting 



