82 Tait 



a minute length of nerve, using 'the thin glass tube previously described, 

 the muscular response tends to be convulsive and not tetanic, while the 

 period of time during which the twitchings continue is not long. When, 

 on the other hand, 2 or 3 cm. of the nerve is frozen in a cold chamber, the 

 cooling being effected by radiation, the muscle tends at first to go into a 

 prolonged tetanus, while the succeeding conviilsive movements may last for 

 many minutes. Whether this difference is due to more rapid freezing in 

 the case where the cooling is by conduction, or whether it depends simply 

 on the shorter length of nerve frozen, I have not as yet determined. 



On looking over my charts, I find that freezing of thick nerves from 

 large-sized frogs is, as a rule, accompanied by more twitching of the muscle 

 than is the case when preparations from smaller frogs are used. Whether 

 this is a general rule or merely accidental I cannot say. 



One thing, however, became apparent during the investigation of the 

 muscular twitchings from freezing of the nerve, viz. that under certain 

 conditions freezing may occur without any twitching of the attached 

 muscle. Previous experiments on the cooling of nerve (9) had shown that 

 conductivity may disappear at temperatures lying entirely above the 

 freezing-point, while in other cases again no such disappearance of the 

 conductivity occurs even though a considerable length of the nerve be 

 cooled right down to any temperature short of the freezing-point. It was 

 a natural idea that, in those cases in which freezing was unaccompanied by 

 muscular twitching, the temperature of such disappearance of conductivity 

 was high ; for then, before the molecular disturbance due to freezing occurred, 

 the nerve for some considerable distance around might be quite incapable 

 of conducting as the result simply of cooling. One or two experiments 

 sufficed to show that this is the correct explanation of the phenomenon. 



Nerves in which conductivity disappears at a high tempera- 

 ture may undergo freezing without any excitation being trans- 

 mitted from the site of the freezing to outlying parts. Other 

 nerves, in which the temperature of disappearance of con- 

 ductivity lies low, are thrown into a condition of excitation 

 throughout their whole extent when freezing occurs. 



Seeing that absence of conductivity in a cooled nerve may arise in two 

 ways, (1) in certain cases as the result of cooling to a temperature still 

 above the freezing-point, (2) as the result of freezing, it is well to clearly 

 distinguish the two conditions. Botanists use the term "cold rigor" to 

 indicate the condition in which function ceases in a plant as the result 

 of cooling when the temperature still remains above the freezing-point. 

 Without committing ourselves to any theory as to the process by which 

 conductivity becomes abolished in a nerve which has not been cooled to 

 the freezing-point, we shall, for convenience, use the term " cold rigor " to 

 denote the condition in question. 



One phenomenon I got to look on as indicative of the near approach of 

 freezing in a cooled nerve. If one gradually lowers the temperature, 



