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Part III. — Twenty -sixth Annual Report 



mechanical, as pinching, cutting, etc., or electrical, such as may be pro- 

 duced by a galvanic cell. This is well seen in the lower vertebrates, such 

 as fish and amphibia. Since the muscles of cold-blooded animals 

 such as fishes are not so closely under, nor so dependent on, cerebral 

 control as those of warm-blooded animals, and since in them metabolic 

 changes are not so active, they exhibit a greater vitality after death as a 

 whole, and retain their property of irritability longer than in higher 

 animals. As rigor mortis can only supervene after the complete cessation 

 of irritability, it is consequently later of appearing and longer of dis- 

 appearing in these animals than in mammals and birds. As the due 

 appreciation of these facts would be invaluable to trawl fishermen, fish- 

 curers, and meat inspectors, and since such knowledge could be utilised 

 on the one hand for the better preservation of fish, and on the other for 

 the inspection of fish, the following simple experiments may be readily 

 carried out, and by doing so, an intelligent and practical acquaintance 

 with this subject may be readily obtained. 



When a newly-caught fish is taken out of the water, as in rod or line 

 fishing, it leaps and struggles about, often with fins erect, and attempts 

 to get back to its natural habitat. These movements gradually diminish, 

 and usually in from 15 to 30 minutes have ceased, and in five minutes 

 more there is usually no response on handling. The fish is now practi- 

 cally dead, but the muscles still retain their power of irritability for a 

 varying length of time, which may extend from 10 to 15 hours according 

 to circumstances, and still respond in the form of contraction to electrical 

 and mechanical stimuli, which may be produced, on the one hand, by a 

 very simple electrical apparatus, and on the other by simply tapping, 

 pinching, cutting, etc. This property of irritability will be found to 

 disappear first in the muscles of the head region, then in those of the 

 trunk, and lastly in those of the tail region. Then, just in the same 

 order from before backwards, the gradual disappearance of irritability is 

 succeeded by rigidity of the muscles or rigor mortis. It is first seen in 

 the muscles of the lowsr jaw and gill covers, when the mouth and gill 

 covers are firmly closed. The stiffening then travels backwards until the 

 whole fish is rigid, and, when complete, the mouth is often gaping widely 

 open. After an interval of time, varying from hours to days, the rigor 

 begins to disappear precisely in the same order as it appeared — first the 

 muscles of the jaws and gill covers, then those of the trunk, and lastly 

 those of the tail region, until the whole fish becomes quite soft and limp, 

 just as it was when removed from the water. 



Such, in general outline, is the sequence of events ; but there are many 

 important factors which exercise a determining influence as regards time 

 of onset, length of duration, and disappearance of rigor in fishes. The 

 most important of these I will state briefly. They are from observations 

 made on a large number of fish, probably several thousands. 



The cause of rigor mortis — the coagulation of the soluble myosinogens 

 of the muscle plasma — is not for the present under consideration. 



It will be found that rigor is later in appearing and lasts longer in 

 the following conditions : — 



A. Fish in season. 



B. Fish in a healthy and vigorous condition. 



C. Fish which are at once killed on capture. 



D. Fish which are not only killed but are pithed at the same time 



— that is, have the brain and spinal chord destroyed. 



E. Fish gutted immediately on capture. 



F. Fish handled as little as possible after capture. 



G. Fish kept at low temperatures, as when iced or kept in cold storage. 



