Whether the heat in an artery is natural or accidental.

One inquires further whether the heat in an artery is natural or accidental.

1. And it seems to be natural. Because for each thing it produces, nature provides something by which it may be preserved. Therefore, it does this too for natural heat. But this is not preserved anywhere other than in an artery, and therefore, etc.

2. In addition, the radical moisture is the food and fodder of the natural heat, whereas superfluous moisture extinguishes it. Therefore, it is necessary that it be preserved in something else away from the superfluous moisture. Therefore, etc.

To the contrary. The arteries arise from the heart. Therefore, that same heat that flows from the heart is preserved in an artery. But one such as this is accidental, and therefore, etc.

One must reply that the artery does not serve the natural heat, but more so the accidental and nourishing heat. And the reason for this is that a natural heat exists in every member. If, therefore, an artery were for preserving the natural heat, an artery would be in every member. But this is not true, and therefore, etc.

1. On to the arguments. To the first argument one must reply that natural heat is preserved in several ways, namely, through the expulsion of superfluities, through ventilation, and through a corresponding warming of the nourishment. And this is why it is not necessary to posit arteries for the preservation of natural heat, because it is preserved in other ways.

2. To the second argument one must reply that natural heat can be extinguished by superfluous moistures. This is why an animal body is porous, so that the superfluities and fumes can be expelled through sweat and through other wastes or products of digestion.

Whether the diaphragm is necessary.

One inquires further about the diaphragm, and whether the diaphragm is necessary.

1. It seems not. A part that divides is not required between members that share their influences with each other. But the spiritual and nutritive members share their influences, because the heart infuses the liver, and the liver the heart, and the diaphragm is arranged between them. Therefore, it is not necessary, because it impedes these mutual influences.

2. In addition, spiritual members do not differ from nutritive members more than nutritive members do from sensitive or generative members. But no part dividing them from one another falls between the nutritive, sensitive, and generative members. Therefore, neither does one fall between the nutritive and spiritual members.

The opposite is clear from the Philosopher's intention. One must reply that according to medical authorities there are four distinct regions in the body of perfect animals. One begins at the top of the head and ends at the root of the tongue, and this is the region of the animal in which the brain rules. The second begins at the root of the tongue and passes through the windpipe to the lungs and heart, as far as the belly and intestines. And this region is called the vital or spiritual region, in which the heart rules. The third region begins at the root of the tongue and passes through the esophagus and the belly, liver, and intestines, and ends at the lower parts of the body. And this one is called the nutritive region, in which the liver rules. The fourth begins from the kidneys and the lower part of the vertebrae, and ends at the anterior parts. And this is called the generative region, in which the testicles rule. But it is the case that there must exist a division among these regions; otherwise, the parts of one would be damaged by the parts of another, since they lead to or are arranged for diverse organs. Therefore, the uvula, because it is a certain membrane that closes the opening to the windpipe, divides the animal and vital regions. And similarly there is a certain membrane called the syphac that divides the generative from the nutritive regions. And the diaphragm is between the vital and nutritive regions, but this one is stronger and larger and more evident than all of the other intermediate webs [telae]. And the reason for this is that undigested vapors rise up from the stomach, which, if they approached the heart immediately, would suffocate it or induce syncopis. And this is why, lest the heart suffer some flaw or injury or failure, either from the stomach or intestines, provident nature arranged a device that would both hold and hold in check, namely, the diaphragm. And this is why it is thicker and denser in the extreme parts at which it is joined to the liver and spleen and ribs, but it is thinner in the middle part which is near to the heart, lest it bear some injury to the heart or lungs on account of its thickness. There is another reason for the diaphragm's necessity, since, if there were no diaphragm, putrid fumes from the corrupted feces would reach the heart and kill it, as [indicated] before, and, moreover, we would always perceive a putrid odor in the nose and mouth, just as we do on the outside, if there were no diaphragm. And therefore, etc.

1. On to the arguments. To the first, one must reply that although the nutritive and spiritual members are divided by a web, nevertheless there are pathways in the web itself that lie open to their influences.

2. To the second argument one must reply that there is a division between the other two regions, just as there is between the spiritual and nutritive regions, and this is why, etc.

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