558 GROWTH IN TISSUE CULTURE 6 



(b) Effects of visible light 



Normal connective tissue cells are not greatly affected by exposure to visible light 

 of the intensities necessary for ordinary observation or even for high power photo- 

 micrography. Goodrich and Scott (1922) were among the first to study this 

 question, and they compared hanging drop cultures of chick heart fibroblasts 

 grown in the dark with similar cultures grown under four days continuous expo- 

 sure to polychromatic light of an intensity of 270 foot candles. They observed no 

 detectable difference. A careful study of the effects of light upon living cells was 

 made by Earle (1927, 1928). Levicocytes responded by increased motility, followed 

 by cellular degeneration. Chick fibroblasts suffered rapid degeneration in the 

 presence of red blood corpuscles (which themselves respond by haemolysis), but 

 irradiation of the fibroblasts for periods of up to 24 h. in the absence of haemo- 

 globin caused only slight damage. There appears to have been no systematic 

 study of the effects of visible light on a variety of cells, which might reveal differ- 

 ences in sensitivity of different cells to different intensities and different wave- 

 lengths. Roffo (1933) detected a greater sensitivity in cells from a rat sarcoma 

 than in normal chick fibroblasts. The effects of visible light of various wavelengths 

 at constant intensity (90 foot candles) upon cells from the chick embryo was studied 

 by Frederic (1954b). Degeneration began after 30 min. exposure to short wave- 

 lengths (436 mfji). With increasing wavelengths, the response was slower, and at 

 556 m^ the effect might be reversible up to 60 min. At 57 1 m[j., the changes took three 

 times as long, and exposure to 623 m[i. appeared to prodvice no effect, even after 10 h. 

 illumination, except acceleration of the mitochondrial movements. The intensity 

 used was about 20 times that required for high power photomicrography, so it is 

 concluded that yellow-green light is perfectly safe for such purposes. 



(c) Effects of ultraviolet irradiation 



Levaditi and Mutermilch (1913b) fovmd differences in response to general 

 ultraviolet radiation between chick fibroblasts and amoeboid cells from the chick 

 spleen; the former were damaged by 20-30 min. irradiation, which had no effect 

 on the motility of the latter. The effects of UV upon chick mesenchyme cells 

 were studied by Mayer and Schreiber (1934), who grew their cultures upon 

 quartz coverslips and exposed them to ultraviolet radiation of 366 mji, - 230 m^ 

 at varying intensities and for varying lengths of time. The longer wavelengths 

 (366 m^) had no effects even after very high dosages. With decreasing wave- 

 lengths, the sensitivity increased. This is in agreement with the general proposi- 

 tion {cf. Loofbourow, 1948; Giese, 1950) that it is the range 200-310 mjx that 

 most readily kills or injures cells, whereas the near UV is innocuous. 



(d) Effects of ionizing radiations 



Cells growing in tissue culture provide excellent material for studying the 

 effects of irradiation upon various cellular functions. Different cell types have 

 very different sensitivities to radiation, and the response varies with the dose and 

 with environmental conditions such as pH, temperature and oxygen tension (Patt, 

 1955). Relatively small doses may slow down the cell multiplication rate, produce 

 mitotic abnormalities or completely inhibit cell division. With increasing doses, 



