127 



tissiio itself. An objection to this theory is that the quan- 

 tity of water which congeals at the first freezing point is 

 often considera])ly greater than that whicli can possibly be 

 extruded in the wounding. 



2. The "Thermal Gradient" theory, suggested to Luyet 

 and Gehenio by the fact that the wave of congelation which 

 moves from the external surface of the object inward and 

 wiiich liberates heat gives rise to a wave of heat whicli 

 travels toward the thermometer. This stops or retards 

 the cooling curve, thus producing an apparent freezing- 

 point. But cases were observed in which the temperature 

 stayed constant at the first freezing point for nearly 10 

 minutes which was evidently more than the time necessary 

 to dissipate a wave of heat, in the conditions of the experi- 

 ments. 



3. The theory of the "Eutectic Point" (Mez and Voigt- 

 lander), which considers the two points as, respectively, 

 the freezing and the eutectic point of the tissue. The ex- 

 tremely high cooling velocities used by these authors in 

 their determinations (c/. Curve 5, Fig. 7) render their 

 results the most uncertain. (For a more detailed discus- 

 sion see below, under Freezing Curves.) 



4. The theory of the "Double Freezing Point," accord- 

 ing to which the 2 freezings are not only apparent and 

 attributable to the procedure or to the apparatus but real, 

 one being the congelation of intercellular, the other of 

 intracellular water (the latter w^ould freeze after extrac- 

 tion from the cells by osmosis or within the larger vacu- 

 oles). Luyet and Gehenio, after proposing the theory, 

 mention its agreement with most of the facts observed : the 

 occurrence of the double freezing in living tissues only, 

 the innocuous effect of a congelation below the first (but 

 above the second) freezing point, the absence of a first 

 freezing in dried tissues, its more frequent occurrence in 

 soaked tissues, the rise of the first freezing point when 

 more water is imbibed, etc. They point out, however, that 

 the existence of two different freezing points, one for the 

 intercellular and the other for the intracellular fiuids would 



