527 



But these histological appearances have but little to do with the 

 physiological phenomena. A muscle may be frozen so as to lose all 

 irritability, and yet preserve its natural appearance. Two muscles 

 may be frozen so that both shall scarcely have a fibre that is not 

 more opake than natural and that has not lost its striae, both, in short, 

 shall be affected anatomically, as far as we can at present tell, to the 

 same degree, and yet one will live and the other is dead. 



In muscles which never regained their irritability, the act of thaw- 

 ing was accompanied by the onset of a peculiar rigor, which differed 

 from the " rigor mortis," and resembled the " rigor caloris " in being 

 an active contraction, i. e. in producing a movement. The hind leg 

 of a frog, when rigor mortis comes on, retains the position it pre- 

 viously had, whether of flexion or extension. Powerful excitation 

 of the spinal cord or ischial plexus produces extreme extension. 

 Plunging into boiling water brings the flexed leg to extreme exten- 

 sion. If the leg be killed by frost in a flexed condition, it will when 

 thawed assume gradually the position of extreme extension : so muscles, 

 frozen singly, shorten when thawed. This contraction is never seen 

 in muscles destined to regain their irritability. I have seen it come 

 on in a muscle which had been frozen for three hours : it is a sure 

 sign of death. This contraction continues after the production of 

 the movement as a peculiar rigidity, which vanishes only when the 

 softening from decomposition becomes apparent. 



The effect of low temperature on the frog's heart is very peculiar. 

 There is a great diminution in the rate of rhythm, and very marked 

 increase in the duration of each systole, so that sometimes the heart 

 is frozen in a tetanic beat, as it were. I have never seen a frozen 

 heart resume its beat when thawed ; but I have often seen one part 

 of the ventricle still beating while another part was frozen quite 

 hard. 



Similar results were obtained by freezing the muscles of leeches 

 and snails. Frozen for a short time they recovered their irritability, 

 for a longer time they died. 



In the latter animals, not only was mere irritability recovered, but 

 I have seen snails, which I had every reason, by examining the state 

 of snails of the same size frozen under exactly the same conditions, 

 to believe had been frozen throughout, regain voluntary motion, and 

 crawl about with extended horns as if nothing had happened. Their 



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