STRUCTURAL AND CHEMICAL ARCHITECTURE OF HOST CELLS 29 



increase of the living world involves the production of more cells and that this 

 rather basic phenomenon calls upon cells to be altering their structures and 

 organization, even their metabolism, as the cycle of growth, division, and 

 growth proceeds. A given cell may be "fixed" by the biologist for the purposes 

 of observation; if it had not been stopped in its tracks, it would almost 

 certainly have been something else soon thereafter. The study of the temporal 

 sequence of biochemical events and their relation to cellular activity is in its 

 infancy; as an example one might point to the dearth of biochemical informa- 

 tion concerning the mechanism of cellular division, although this subject is 

 beginning to be explored more actively. 



In most instances, however, the existing analyses of cell structure are 

 undefined with respect to the life history of the specific cell being studied; 

 most commonly, various structures will have been isolated from a hetero- 

 geneous cell population of which like members will have been in different 

 stages of their division cycle. ^ We are compelled to proceed despite the 

 existence and recognition of this deficiency. 



It is possible that the very process of obtaining homogeneous populations 

 of cells in the clonal development of microbes or animal cells tends to em- 

 phasize the properties of the cidture rather than the attributes of individual 

 cells, which are, after all, the units of infectability of virology. From an 

 inoculum of relatively few cells or even only one, selected to insure genetic 

 homogeneity of the progeny, a large culture may be produced in which the 

 cycle of growth, division, and growth is reproduced many times. In many 

 instances, rajDid grow^th rates involve concomitantly a maximum efficiency in 

 the production, utilization, and assembly of metabolites. One gets the 

 impression of a weU-ordered balance in the course of cellular synthesis and 

 duphcation, of an extreme interdependence of parts in such experimental 

 systems, in which biological variability has been minimized. This is in con- 

 trast to the functional separation of growing parts from dividing parts, which 

 is readily seen in differentiating and differentiated cells. Such cells of this 

 latter type exist in adult tissues or in certain phases in microbial cultures; 

 they are usually difficult to handle and to maintain in these states. Their 

 physiological and genetic variability tend to be maximal; as a consequence, 



^ The recognition that such material is imsatisfactory for many biological purposes 

 cannot help but produce a tremendous growth of biological study on the production of 

 homogeneous cell populations, as virology has already demanded of tissue cultures. This 

 will also extend to the production of synchronous cell division and controlled life 

 cycles, even as effected in Nature during the early development of various embryological 

 systems. That Nature has already provided some materials ready-made for such bio- 

 chemical studies calls to mmd the comment of Sir Frederich Gowland Hopkins, who 

 asserted that in explormg and cultivating the fields of Natiire, the chemists were best 

 provided with the machinery for this cultivation, but that the biologists knew best the 

 lay of the land. 



