2 FUNDAMENTALS OF CYTOLOGY 



lenses were probably first used seriously as optical instruments sometime 

 in the eleventh century, while the first compound microscopes (and 

 telescopes) were devised at the end of the sixteenth and the beginning of 

 the seventeenth century. A number of models of simple and compound 

 instruments soon became available, and these in the hands of many men, 

 professional and amateur, made possible a number of researches on the 

 minute anatomy of living beings that still excite our admiration. 



Even when aided by the microscope, however, vision is limited. As 

 long as the objects studied lie within the visible range, direct observation 

 with or without the aid of lenses may suffice, but when they are smaller 

 than this, one must employ the very different analytical methods famil- 

 iar to the chemist' and physicist. With these methods have been devel- 

 oped clear concepts of minute structure in terms of molecules and atoms. 



Obviously the organism confronts the worker with many problems 

 which require more than one mode of approach. For example, in the 

 study of the development of an embryo or the process of secretion in a 

 cell one encounters structural alterations visible with the microscope, 

 while accompanying these are invisible alterations in functional activity 

 that must be investigated by chemical means. The question of the rela- 

 tive priority of functional and structiu'al change is frequently debated, 

 but, if atoms and electrons could be as easily seen as muscles and cells, so 

 that every functional reaction would appear also as a visible change in 

 molecular structure, the question as stated would probably not arise. 



Every major biological problem thus comprises several partial prob- 

 lems which must be solved through the use of different techniques. One 

 can no more solve such a major problem with a single technique than a 

 carpenter can build a modern house with a single tool. The fact that the 

 organism sets such complex problems before us began long ago to resolve 

 the science of biology into a number of ''fields," each of them charac- 

 terized by a particular class of observations to be made and hence by a 

 particular set of requisite techniques. Morphologists, physiologists, and 

 taxonomists, for example, asked the organism for three different classes of 

 data, and they employed three different methods of inducing the organism 

 to yield them. This diversification of the science, which proceeded 

 rapidly in the nineteenth century, gave rise to groups of specialists who 

 scarcely understood the language of other groups, yet all agreed in 

 employing one general underlying method- — the scientific method of 

 controlled observation, formulation of hypotheses, and verification. 

 Upon this method they will continue to rely, for it is chiefly responsible 

 for the rapid increase of dependable biological knowledge in recent times. 



Cytology. — Cytology as a specialized branch of biology arose from 

 attempts to see more clearly the microscopic structure of plants and 

 animals. That the tissues of organisms have a cellular organization was 



