356 TISSUE CULTURE 



Other Types of Flasks. The walls of the ordinary Carrel flask 

 are too thick for oil immersion observation of the culture. Recently 

 Carrel has devised a micro-flask of similar shape, 3 cm. in diameter 

 with the horizontal surfaces remarkably flat and of average 

 coverslip thickness. Another type of flask is provided with a large 

 hole in its base over which a circular coverslip can be accurately 

 sealed. Oil immersion observations are easily made with both 

 these types of flasks. 



McJuNKiN (Archiv. f. exper. Zellforsch. iv, 1927, p. 122) 

 describes a simple method for making ordinary flasks from test- 

 tubes. As the clotted medium containing the explants is not easily 

 removed from Carrel flasks without breaking them, Doljanski 

 {ibid., xiii, 1932, p. 717) has invented a particularly useful 

 pattern which has the shape of a Carrel flask, but with its base 

 consisting of a detachable circular glass plate. This plate fits 

 closely to a ground basal rim on the flask, and is sealed to it by a 

 thin film of egg albumen. 



789. Cultures in Watch Glasses. This method has been used 

 with great success at the Strangeways Laboratory, Cambridge. 

 Larger explants are imbedded on the surface of a large plasma 

 clot in a watch-glass and bathed in very dilute embryonic extract 

 which restricts the uncontrolled growth of migrating cells. The 

 whole is then sealed in a Petri dish containing moist cotton-wool. 

 Organotypic growth of entire early embryos, embryonic organs 

 and skeletal fragments is best obtained by this technique. 



790. The Continuous Irrigation Technique of de Haan (Durch- 

 stromungsapparat). This is a more elaborate arrangement whereby 

 the culture is constantly irrigated by fresh nutrient medium. 

 More recently the apparatus has been modified by including 

 devices for saturating the fluid medium with a controlled gas 

 mixture and hence adjusting the pH. Space does not permit the 

 detailed description of this apparatus and its several modifications ; 

 see DE Haan, Bull. d'Histol. Appl., iv, 1927, p. 293 ; Suy, ibid., 

 viii, 1931, pp. 210, 294 ; Julius, Acta brev. Nederl., ii, 1932, 

 p. 69. 



791. The pH and Gaseous Environment of the growing culture. 

 Mention has already been made of Carrel's simple method of adding 

 phenol red to the culture medium and introducing COg in varying 

 concentrations into the flask for control of the pH. More elaborate 

 methods are given by Earle {U.S. Pub. Health llept., xlvi, 1931, 

 p. 1997 (hanging-drop cultures) and p. 2668 (flask cultures) ). 

 Cf. also Earle {Archiv. f. exper. Zellforsch., xvi, 1934, p. 116). 

 See SciiADE {ibid., xv, 1934, p. 121 for the cultivation of tissues in 

 a constant gas mixture. 



The roller-tube apparatus described by Gey {Amer. Journ. 

 Cancer, xvii, 1933, p. 752), consisting of a revolving drum contain- 

 ing a series of glass culture tubes, provides for the constant 



