It is to this insulation of the vitality of the organs by their surrounding cellular texture, that we can refer in part that of the diseases, which is only an alteration of this vitality. Every day we see an affected part contiguous to a sound one, without communicating to it its disease. A healthy pleura covering the lungs filled with tubercles, or ulcers, in phthisis; an inflamed peritoneum corresponding with the intestines, the stomach, the liver, the spleen, which remain in their natural state; the mucous membranes affected with catarrhs approaching without danger the numerous parts they cover; the sub-cutaneous organs remaining free from the innumerable eruptions of which the skin is the seat; the tunica arachnoides in a state of suppuration enveloping a healthy brain, and a thousand other similar facts; these are the phenomena that the examination of bodies constantly presents. Shall I speak of the different tumours that are formed in the midst of organs, without their perceiving it, of the numerous excrescences that grow by their side without affecting them? Dissect a muscle under a suppurating cutaneous wound, or even a most obstinate ulcer; you will not often find it different from the rest, the skin only has been affected. No doubt the difference of vitality of two neighbouring organs is an essential cause of the insulation of their diseases; but the cellular atmosphere that protects them is also an important one. When an organ sends elongations into another, it communicates to it much more easily its diseases, than if a thick cellular layer separated them; for example, we know that the affections of the periosteum and the bone are soon identified. Let us not, however, exaggerate this idea, by describing the cellular atmosphere as an insurmountable barrier to diseases. Facts would often contradict us, by showing diseases passing from an organ to the texture that surrounds it, and from this texture to the neighbouring organs; so that we see it at one time an obstacle, and at another the means of their propagation. The atmosphere that is formed is in different cases susceptible of being charged with all the emanations that arise from the organ, or to speak in language more strictly medical and physiological, the vital forces of an organ being altered, those of the surrounding texture are often altered by communication, and gradually those of the different neighbouring organs themselves. This kind of influence that the organs have upon each other, should be carefully distinguished from sympathy, in which, a part being diseased, another part becomes affected without the intermediate ones being deranged in their functions. Here there is constantly in the communication of diseases, the same order as in the position of the organs.