ZOOLOGY. 391 



Experiments have lately been made to determine if the introduction of air 

 into the chest, through the respiratory passages, with great force, does not 

 have some influence upon the action of the heart ; and it has been found that 

 there is a diminution in the frequency of the heart's action, sometimes to 

 such an extent, that the pulsations amount to only two-thirds the normal 

 number. 



The explanation which has been given to this phenomenon is based upon 

 mechanical grounds, but M. Sequard thinks, if this explanation be correct, 

 it is so only to a certain extent. One other cause at least, that of a nervous 

 influence, he has demonstrated to exist. 



It is well known that some mammals resist asphyxia for a long time, 

 making efforts to breathe, often for several hours when the entrance to the 

 lungs is closed. Now it is found that when the chest of an animal in this 

 condition is opened and retained in such a position that there can be no 

 motion and no mechanical action, the diminution of the pulsations persists. 

 The phenomenon is then due to the action of the par vagum nerve. It is 

 found that when this nerve is irritated at its root or galvanized, the action of 

 the heart is arrested ; in this respect differing from the other muscular organs, 

 which are excited to action by irritation or galvanization of their nerves. 

 When the chest is opened, without injury to the par vagum, there is seen to 

 be a control over the action of the heart during inspiration. But if the par 

 vagum of both sides of the chest be cut across, this control is lost. There is 

 good ground for belief, therefore, that at every effort of inspiration, there is 

 a transmission of nervous influence along the par vagum to the heart, acting 

 as a check upon it and regulating its action, and thus preventing the increase 

 of pulsation, which might otherwise go on, in increased ratio to infinity, 

 under the excitement of forced respiration. 



It has been said that people have killed themselves by stopping the heart's 

 action. One of the brothers Webber, of Leipsic, found that when an effort 

 was made to contract the chest during a full inspiration, that there was great 

 suffering, fainting, and almost death. Webber himself nearly lost his life 

 trying the experiment. By irritating the various organs which receive 

 branches from the par vagum, as the stomach, spleen, etc., by galvanizing 

 them or crushing them at once by a blow of a hammer upon an iron surface, 

 it is found that the heart's action is diminished in frequency, and in some 

 instances entirely suspended. Cases of sudden death from a blow upon the 

 stomach, externally, are to be attributed to the same cause. The action upon 

 the heart from overloading the stomach, either with too much solid or liquid 

 matter, is to be explained also by the influence of the par vagum upon the 

 heart. 



Dr. Se'quard al-o referred briefly to his researches upon the Supra-renal 

 Capsules. These two small organs, lying in immediate connection with the 

 kidneys, have been considered very unimportant until within a few years. 

 Now it is found, that when thev are removed from the bodv of a hvino- ani- 



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mal, there occurs a very great change in the blood, and the animal dies in a 

 short time, sooner even than after the removal of the kidneys. There is 



