On the other hand, as the arteries have not sensible organic contractility, hardly any animal sensibility, and but little tone, the other organs can with difficulty develop in them sympathies by their influence; for, in order that a vital property should be brought sympathetically into action in a part, it is necessary that it should exist there, and even be conspicuous. Thus the innumerable variations of the pulse, which are the product of sympathies, have all essentially their seat in the heart; the arteries are not connected with them. Now the sympathies make the heart contract or arrest its motion, as stimulants or sedatives directly applied to it, that is to say, by acting on its sensible organic contractility. When an aneurism is broken in a fit of anger, or in the act of coition, a case of which I have seen with Desault, it is the motion of the blood, which is suddenly increased, that is the cause of it; it is not the arterial texture that has been affected by the passion. Besides, upon what can the sympathies act in the arteries? It could not be either upon the elasticity or the contractility of texture, the only properties, however, capable of contracting these vessels. Observe, also, that the sympathies put in action only the vital properties, because they are themselves a phenomenon purely vital. The physical properties and the properties of texture cannot be exercised under their influence; this is an important observation. Besides, as the arteries are every where spread in the organs, and as they form, if we may so say, a part with them, it would be difficult to distinguish what belongs to them, especially as it respects sensibility, from what is peculiar to these organs. ARTICLE FIFTH. DEVELOPMENT OF THE VASCULAR SYSTEM WITH RED BLOOD. I. _State of this system in the Fœtus._ The fœtus differs essentially from the infant that has breathed, in this, that its two great vascular systems in reality form but one, since the foramen ovale on the one hand, and the ductus arteriosus on the other, form a direct communication between the two. This communication is much more evident at the period nearest conception; these openings contract towards the period of birth. 1st. The foramen ovale is formed, in the first months, by two productions in the form of a crescent, whose concave surfaces are opposite, and leave between them an oval space, which is constantly contracting, because these two productions constantly approximate and have a tendency to cross each other, which in fact takes place after birth. 2d. The ductus arteriosus contracts as the pulmonary artery dilates.