CHAPTER III 



THE VITREOUS STATE, VITRIFICATION, 

 DEVITRIFICATION AND VITROMELTING 



The subject of this chapter is new in biology. The first 

 experiments on '* Vitrification of Protoplasm" were re- 

 ported by Luyet in 1937. Since the data are still scarce, 

 instead of following our usual procedure which consisted 

 in selecting the essentials in the literature, we shall at- 

 tempt to give, in compact form, a complete account of the 

 experiments made up to the present (May 1939) and shall 

 supplement it with some observations and remarks sug- 

 gested by our own experience with the subject. 



The first part of this chapter will be devoted to a study 

 of the principles, facts and methods relating to the vitre- 

 ous state in physical systems, and the second wdll treat of 

 the application of these principles and methods to biologi- 

 cal material. 



I. PHYSICAL SYSTEMS 



1. The Vitreous State. The vitreous state has been 

 known in silicates for hundreds of years, but it was gen- 

 erally assumed that the possibility of becoming vitreous 

 was an exceptional property of these bodies. At the end 

 of the last century (1898), Tammann pointed out that a 

 large number of substances can be obtained as glasses and 

 suggested that this property might be universal. Out of 

 a series of 153 carbon compounds investigated, 59, that is, 

 38 per cent, could be vitrified. 



The production of the vitreous state is conditioned by 

 temperature in the manner illustrated in the diagram. Fig. 

 29. If the temperatures are plotted on a horizontal line, 

 from the absolute zero up, the states, gas, liquid, crystal- 

 line and vitreous, are represented by the zones 0, L, C, V, 

 and the changes of state by the zone D and the points ]\[ 

 and B. Upon a lowering of temperature, a body in the 

 gas state becomes liquid at the liquefaction point B, it 

 thereafter crystallizes at the freezing point M and stays 



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