Page:Philosophical Transactions - Volume 002.djvu/144

 Lungs with the point or edge of your Knife. This done, put in your finger, and with your nail separate the Nerve, which passeth along the side of the Pericardium toward the Diaphragme. Then put in a Probe, a little inverted at the end like a Hook, and apprehend the Nerve, and pull it to the Orifice of the Breast, and cut it off, and sow the hole up very close. Do the same on the other side, and presently let the Dog loose, and you will plainly see him draw his breath exactly like a Wind-broken Horse: Which yet you will see plainer, if you run him a little in a string after he is cut. But that any one may perform this Experiment the easier, let him first take notice, how the Nerves of the Diaphragme pass along on each side of the Pericardium in a dead Animal, before the Trial be attempted in a living one.

The most obvious Observations from this Experiment, are,

1. That the whole manner of Respiration is quite alter'd. For as in a sound Animal, in Inspiration the Belly swells by the lifting up the Bowels by the Contraction of the Diaphragme; and in Expiration the Belly falls by the Relaxing of the same: In a Wind-broken Dog or Horse 'tis quite contrary; for in them it is to be seen plainly, that when they draw their breath, their Belly is drawn in very lank and small, and when they breath up, their Belly is relaxt and swells again.

2. It being certain, that the Lungs do not move of themselves at all, but wholly depend upon the Expansion of the Thorax by the Intercostal Muscles, and the Diaphragme; by this Experiment it doth appear, how much the single motion of either of them doth particularly contribute to Respiration. For all Inspiration being made by the Dilatation of the Thorax, and that Dilatation being caused partly by the Intercostal Muscles drawing up the Ribs, and partly at the same time the Diaphragme by its Contraction drawing downward the lower small Ribs to which 'tis joyn'd, and also lifting up the Viscera of the lower Belly, by which they do jointly make all the space they can for the Air to come in and distend the Lungs: It must hence necessarily follow, that the Intercostal Muscles and the Diaphragme being constituted for two distant Employments (though both to the same end) and neither being able to perform the others Office, where one ceaseth from its work, the other for the exigence of Nature mull take more pains to supply