TISSUE CULTURE 



77 



human being growing for over half a year. A recent successful 

 growing of human tissue in culture is that of Vogelaar. He has 

 grown human liver and thyroid glands from a three months' 

 embryo (Fig. 61), 



Cells in culture are most often studied as living material, yet 

 they may be killed and stained, and further observations of value 

 made upon them (Figs. 56, 63). 



The types of cells which are to be found in a culture (e.g., of a 

 chick embryo heart) are numerous. The best kno\Mi and most 

 striking are the fibroblasts (Figs. 59, 62). It is these which 

 Carrel has had growing for twenty-three years. They are among 



Fig. 62. — Drawing (semidiagrammatic) of a fibroblast. 



the largest of tissue cells, distinguishable by size, mode of colony 

 formation, nature of surface, cytoplasmic elements, appear- 

 ance of nucleus, angular shape, and long protoplasmic processes 

 formed as they move. Almost as abundant are the monocytes 

 and macrophages, types of blood leucocytes. They are 

 less angular, more active than fibroblasts, have undulating mem- 

 branes, a very different locomotion, and are independent. 

 Other types of cells occurring in culture are muscle, nerve, and 

 epithelium. 



The appearance of a cell may be greatly changed by its inclu- 

 sions, which, in addition to the nucleus, include five main types 

 (in cells from the chick-embryo heart), viz., vacuoles, neutral- 

 red vesicles, neutral-red granules, fat globules, and mitochondria 

 (Fig. 63). The number and distribution of these cause quite 

 different appearances in the cells. The granule-like inclusions 

 are often massed close to the end of the nucleus (Fig. 62). Such a 

 region Carrel and Ebeling have termed the "digestive area." A 

 starved cell shows no such aggregation of food and waste products. 



