Freezing of Nerve, with Special Reference to Fatigability 81 



compression applied from the exterior to a normal nerve may temporarily 

 abolish conductivity. On physical grounds it is improbable that the out- 

 side coating of ice nips the nerve. A hollow cylinder of water undergoing 

 freezing would expand and not contract. 



Observations made by botanists on the freezing of plant tissues (7) show 

 that crystals of ice become deposited first of all between the cells, and only 

 at a later period, when the temperature is still further lowered, inside the 

 actual cells. Although there are no observations published, so far as I am 

 aware, on the histological appearances inside frozen nerve, we cannot imagine 

 that the solution of salts inside the nerve becomes suddenly solid throughout. 

 Once freezing starts the water is probably extracted from the surrounding 

 solution by degrees, thus raising the concentration of the salts in the non- 

 frozen portions. To any definite fixed temperature below the freezing- 

 point there would probably correspond a definite concentration of the 

 solution in the still fluid portions, while only at a very low temperature 

 would the nerve be solid throughout. The twitchings would, from this 

 point of view, correspond rather to the twitchings that occur in a muscle 

 when its nerve is dried. 



At one time it seemed as if some light might be thrown on the freezing 

 process by a study of the muscle twitchings which ensue upon freezing of 

 the nerve, for at first I imagined I could detect a correspondence in the 

 behaviour during freezing of two preparations from the same frog. 

 Further investigation, however, showed that such a correspondence, even 

 when all precautions are taken to make the conditions similar, is much less 

 constant than I at first thought. 



Another method of investigation which occurred to me was to subject 

 some frogs before dissection to continuous evaporation. Durig (8) found 

 that frogs may lose in two to three days, by evaporation, from 20 to 30 pei- 

 cent, of their weight : in one case he succeeded in diminishing the weight 

 of a frog by 39 per cent, without killing it. In the process of drying a 

 great concentration occurs in the body fluids, the concentration being least 

 marked in the brain and heart of the animals. On the assumption that 

 the nerves might participate in this drying-up process, I took a number 

 of frogs and, after weighing them, placed them in an open wire cage outside 

 the laboratory window. The outside temperature was but a few degrees 

 above zero, and yet in eighteen to forty hours they had lost from 12 '8 per 

 cent, to 23 per cent, of their body weight. Preparations were examined in 

 various conditions of dryness, care being taken not to moisten the nerve 

 with saline solution before freezing. Except that one case, viz. the one 

 which was least dried, showed a more markedly tetanic and longer-lasting 

 response than usual, the muscle twitchings were not different' in character 

 from those in ordinary cases. Apparently little help can be got from this 

 method of investigating the question. 



The character of the muscle response during freezing of the nei've 

 depends to a large extent on the method of freezing. When one freezes 



VOL. I. — JAN. 1908. 6 



