During adult life many though not all tissues of the rat continue to increase in size through cellular proliferation. For example, neurones show no evidence of mitoses whereas in the intestine mitotic activity of the lining epithelium is so great that the epithelial cell population is replaced once in three days. [...]

In 1891, 7 years before Camillo Golgi discovered his famous apparatus, Ramon y Cajal experienced one of his "most deplorable disappointments". While manipulating heavy metal impregnation techniques, he happened to immerse pieces of rat cerebrum in a potassium bichromate-gold chloride solution, and saw a selective reduction of gold salt in an intracellular apparatus, then unknown. [...]

The structure and development of the vertebrate dentition has received the attention of histologists almost since the invention of the microscope. The literature dealing with the structure and fOrmation of teeth was reviewed in great detail by Lehner and Plenk (1936). Their bibliography contained references to well over 2000 individual papers representing the contributions of over 800 authors who had attempted to ellucidate the complexities of the structure and of the mechanism of formation of teeth. [...]

In scientific discourse aging implies "a determined chain of events occupying a significant portion of the lifespan after maturity" (Birren, 1959). This definition suggests changes within an organism, or object, with time. Another term used quite frequently is "senescence", defined as "a process of unfavorable progressive change, usually correlated with the passage of time, becoming apparent after maturity and terminating invariably in death of the individual" (Lansing, 1951). [...]

The role of the thyroid gland in fish is little understood, while it is well known in mammals, birds and amphibians. Thus, in mammals and birds this gland controls the metabolism. In many amphibians the thyroid is responsible for the metamorphosis occurring at the transition from an aquatic to a terrestrial environment. [...]

Growth is the process by which an organism or part of it increases in size. Growth requires an increase in the amount of cell material as well as of intercellular substances, fibres, secretory material, etc. The cells are the significant element, since they produce the intercellular material. And, therefore, growth must involve either an increase in the number or in the size of cells. [...]

This study of the arterial supply to the ureter was made because of the prevalence of injuries to the ureter in pelvic surgery and gynecologic complications to the ureter and kidney following pelvic intervention. [...]

Removal of the thyroid is not always followed by the impressive group of symptoms described in text-books of Endocrinology. In fact, thyroidectomized rats fed on the commercial diet, Purina Fox Chow, do not show the stunted growth and cretinoid syndrome associated with thyroidectomized animals. [...]

The organs of the adult animal may generally be divided into two broad groups on the basis of their mitotic activity. In one group, including liver, kidney or adrenal medulla, mitotic division of the parenchymal cells occurs very rarely. In the second group, comprising the hemopoietic tissue, gastric and intestinal mucosa, epidermis and other tissues, there are numerous dividing cells even in the mature animal. [...]

The occurence of polyploidy in the mammalian hepatic parenchyma had been frequently reported and this phenomenon has been studied mainly in the rat and mouse. The liver contains diploid cells at birth, and in the course of post-natal development, polyploid cells accumulate with increasing frequency until diploid cells are in the minority. [...]