Depression of the melting point of liver tissue rapidly frozen by liquid nitrogen during life provides a means by which the molecular concentration within liver cells may be compared with that of solutions of sodium chloride or of blood or of blood serum.
The rising temperature of frozen blood of guinea pig under the conditions of these experiments is retarded when melting occurs, pursues when plotted a prolonged linear course, and finally rises precipitously at –0.54°C. when melting is complete. With the melting of blood serum of guinea pig and of blood of cat and of rat, the temperature takes approximately the same course. The temperature changes are nearly the same as those of a frozen solution of sodium chloride isotonic with blood serum.
The temperature changes of frozen liver assumes when plotted a linear course at about –1.1°C., increases at intervals with step-like progress and finally rises precipitiously at –0.76°C. The temperature changes in melting liver of cat and of rat are similar. The melting of liver begins at a level which approximates that of a solution of sodium chloride isotonic with it.
The step-like course of temperature changes which occur during the melting of frozen liver are best explained by the assumption that the cells contain substances which successively and temporarily retard the rise of temperature.