No abstract

The rat stomach may be divided into two main regions: the forestomach, a non-glandular region lined by stratified squamous epithelium, and the glandular stomaclr, which consists of two parts, "body" and "pylorus." On examination of the mucosa lining the "body," a number of cells may be found undergoing division. The present work is an attempt to clucidate which cells types are dividing arid what their fate is. METHODSTwo experiments were carried out, a preliminary one to examine whether or not mitoses are present in the mucosa of the body of the stomach at various times of the day, and the main experiment to determine which types of cells are dividing and at what rate. Adult male rats weighing around 200gm were used in both cases. Histological m eth o'ds

No abstract

No abstract

Classical genetics has associated the rigid transmission of hereditary characters with the constancy of the chromosome pattern. Modern work has shown that the chromosomes contain the substance desoxyribonucleic acid (DNA), which is believed to be the carrier of genetic potential. In general, the amount of this material present per cell is constant in all organs and tissues in a given species. Furthermore, isotopic work with a DNA precursor, phosphorus, showed that it does not enter the DNA of tissues in which the cells do not divide—a result interpreted as supporting the classical concept of the stability of genetic material. It was known, on the other hand, that phosphorus is incorporated into the DNA of tissues containing cells undergoing division—a result interpreted as being due to the synthesis of DNA associated with cell division. Evidence is presented to indicate that such synthesis does occur, but is far more extensive than was hitherto suspected, since it involves the complete replacement of all the DNA present before initiation of the cell division. How the cell can safeguard the stability of the genetic material in the course of this total DNA renewal can only be surmised at this time.