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the quantity of which becomes much increased during asphyxia. 

 The relations between these contractions and asphyxia are evi- 

 dent. A great many of them do not exist unless asphyxia 

 exists, and their energy is always in proportion to the degree of 

 asphyxia. 



I believe that the substance in the blood which has that power 

 is the carbonic acid. In admitting this opinion we can easily 

 explain all the phenomena. 



There are certain contractions which take place in muscles of 

 animal life, after death, and which have quite another cause. In 

 the cold seasons, it is not uncommon to find, in limbs of frogs, 

 when we separate them from the body, apparently spontaneous 

 contractions, lasting sometimes for half an hour or even more ; 

 but these contractions have begun when we have cut the nerves, 

 and they continue on account of galvanic discharges which ac- 

 company them. The fact that they begin after the excitation of 

 a nerve, is sufficient to show that they are not like the other con- 

 tractions, of which I have previously spoken. 



Some of the facts I have related may appear to be distinct 

 from the others. So, for instance, contraction taking place in 

 paralysed muscles of the face or of the limbs in living animals, 

 might be considered as quite different from the contractions exist- 

 ing after death. I think that they originate from the same cause, 

 viz., an excitation by carbonic acid. A muscle may be moved 

 or not be moved by an excitant. If the degree of irritability is 

 greater in one case than in another, we may see the same amount 

 of excitation produce a movement in the first case, and not in the 

 second. If the amount of excitation increases, then we may see 

 both muscles moved, but the most irritable more than the other. 

 This is sufficient to explain why the paralysed muscles may be 

 moved by the carbonic acid existing in the blood during life, 

 while the muscles that are not paralysed are not moved. I have 

 found that the degree of irritability increases, during a certain 

 time after paralysis, in the muscles of animal life. Their irrita- 

 bility being augmented, they are excited sufficiently to contract, 

 by a quantity of carbonic acid which is not sufficient to act on 

 the other muscles. 



The following facts and reasonings will, I believe, prove that, 

 at least in the bowels, black blood, very likely by its carbonic 



