The precise seat of calcareous deposit, in respect of the coats of the tubes, has been made matter of much disputation. We have ourselves found that in the aorta the new matter is thrown out between the middle and internal coats, and in the vessels of the limbs either in this situation or in the actual sub stance of the middle coat ; — or, to use the language which the modern anatomy of arte ries would require us to adopt, we should say that the saline matter is deposited in the aorta in the striated and longitudinal-fibrous tunics between the epithelial and circular-fibrous tunics ; and also, in the arteries of the limbs, in the substance of the circular-fibrous and true elastic coats.
There are three kinds of deposit, of com mon occurrence in the arteries, set down by writers as the nidus in which saline accumu lation may occur: these are the " atheromatous matter," the " white spot," and the " cartila ginous patch." The origin and nature of these !natters require to be briefly examined.
The atheroma of the arteries and cardiac valves is a yellowish matter occurring in minute' particles, hardly larger than grains of sand ; separate or clustered into small patches ; most abundant at the points where vessels are given off' from the affected trunk ; obviously' seated underneath a coating of epi thelium, and even probably under the striated tunic of the artery, (as when an attempt is made to peel it away by raising these two coats, it is in part removed with them, and remains partially adherent to the deeper seated tunics); and distinctly unctuous to the feel, when accumulated in any quantity. The substance is indeed of fatty nature. Gluge* found that " an enormous deposition of fat globules solely and alone constitutes this mor bid state, and in fact even with the naked eye a remarkable similarity may be perceived be tween the atheromatous state and certain forms of fatty deposition in the liver." Mr. Gulliver -I- has independently ascertained the same fact, and illustrated his description by figures. I The researches of M. Bizot have very clearly established that this atheromatous matter be comes, with the progress of things, the seat of one or other of two series of changes, termi nating in the one instance in ulcerous soften ing, in the other in calcareous deposition. The stages of the ulcerous softening are four : in the first the yellow matter becomes slightly prominent on the surface of the vessel, and the superficial fibres of the " middle " tunic lose their natural consistence ; in the second the internal membrane is raised into little emi nences by the accumulation of a matter which is sometimes liquid and puriform-looking, sometimes floury and dry, and occasionally containing tninute shining scales, some of which have a white and silvery look (choles terin). In the third stage depressions with a
smooth surface, (except in the points where the lining tunic has undergone fissure for the evacuation of the matter described,) mark the previous seats of this matter. The fourth stage is distinguished by the disappearance of the lining membrane in the affected points, and hence by actual excavation. Neither suppura tion nor injection attend the changes reviewed.
When the atheromatous matter undergoes the calcareous change, a hard but minute point commonly appears in its centre; this gradually increases, especially in breadth, the middle coat being earlier unplicated than the lining tunic, which is occasionally covered with con crete fibrin. Eventually the lining coat is de stroyed, and the concretion brought into con tact with the blood ; the middle coat rarely becotnes affected through its entire thickness. The deposition may commence in a multitude of minute points sirnultaneously, whence the atheromatous matter acquires a gritty feel.
The white and cartilaginiform patches are not in any instance the nidus of the saline deposit, according to M. Bizot ; at least he has never succeeded in tracing the early pro cesses of deposition in those patches. Nothing, however, he admits is more frequent than the deposition of atheromatous and subsequently of calcareous matter underneath the " cartilagi nous " patch, which is occasionally perforated by the calcareous substance, and an appear ance produced easily explaining the current opinion that the patch in question is the ori ginal seat of the saline particles,. We agree with M. Bizot that the " cartilaginous" patch is altered plastic matter exuded on the inner surface of the vessels. Mr. Gulliver has, it is true, discovered fat-globules and crystals of cholesterin in the " white patch " of vessels ; but the circumstance appears explicable in the manner just referred to as resulting from the French author's inquiries.