ZOOLOGY. 265 



the medulla dblongata. To ascertain if it is so, I have made experi- 

 ments on newly-born animals, and on birds. As I have already pub- 

 lished some of the results of my researches on newly-born animals, and 

 as these results are not so completely decisive as those of my experi- 

 ments made on birds, I will merely give here a summary of what I 

 have seen in these last animals. I have found the same facts in ducks, 

 geese, and pigeons ; but as I have repeated the experiments more fre- 

 quently on the last-mentioned animals, I will speak of them only. 

 When their abdomen has been widely opened and their heart exposed 

 to sight, pigeons may live, as it is well known, for a long while. I wait 

 until they are almost dying, having only one, two, or three inspirations 

 in a minute, and then, if the weather is cold, and if the animal has 

 lost many degrees of its temperature, I find that, at each effort it 

 makes to inspire, the heart either almost suddenly stops, or beats much 

 less quickly. 



I have frequently seen the heart completely arrested for five or ten 

 seconds, and twice for twenty or twenty-five seconds, in cases where 

 there was only one respiration in two minutes. This stoppage of the 

 heart's movements was the more remarkable, as they were at the rate 

 of more than two hundred in a minute when the effort at inspiration 

 took place. To decide that it was in consequence of an influence of the 

 par vagum that this occurred, I divided this nerve in the neck, and 

 then found that there was no more influence of the inspiration on the 

 heart, or if there was, it consisted in an augmentation of the frequency 

 of the movement of this organ ; an augmentation due to the shaking 

 of the heart when the chest dilated. 



Sometimes, when the heart was very irritable, and when the efforts 

 at inspiration were still frequent and not energetic (the par vagum be- 

 ing undivided), thesd efforts were accompanied, or rather immediately 

 followed, by an increase in the strength of the heart's movements, 

 probably caused by the shaking. But always when the inspiratory 

 efforts were energetic and rare, they coexisted with a diminution or a 

 momentary cessation of the heart's contractions ; and always in these 

 cases the section of the par vagum has destroyed the diminishing influ- 

 ence of the respiratory efforts on the heart. It would be easy to show 

 that the influence of the inspiratory effort on the central organ of cir- 

 culation is comparable to the change taking place in the pupil when 

 the globe of the eye is drawn inward ; it is an associated action. 



From the facts I have found in the case of newly-born animals and 

 birds, and from the facts observed in man by Professors J. Miiller, 

 Donders, and others, it results that, during efforts at inspiration, a ner- 

 vous influence passes along the par vagum from the medulla oblongata 

 to the heart, diminishing the movements of this organ. And, as by an 

 action of our will we may inspire with energy, it follows that we can 

 by an influence of our will diminish the action of our heart, just as we 

 can contract our pupil by drawing our eyes inwards. 



CIRCULATION OF POISONS IN THE SYSTEM. 



A London physiologist, Mr. Blake, has lately developed some inter- 

 esting results, by experiments in regard to the rapidity with which the 

 various poisons disseminate themselves through the system, and prove 

 fatal. We must not be understood, however, to suppose that these 

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