Early diagnosis of rabies procurable by microscopical examination of the cord. There is a diffuse chromatolysis affecting all the cells, followed by a retraction of the cells from the capsules and a prolifer ation of the cells of the capsule. These press on the degenerating ganglion-cell, destroy it, and fill up the space occupied by it. The chromatolytic changes are best seen by Nissl's stain and the capsu lar changes by hannatoxylineosin. M. P. Ravenel and D. J. McCarthy (Proc. Path. Soc.. July, 1900; Med. News, Aug. 25, 1900).
If, after microscopical examination of the spine and bulb, no perivascular or pericellular miliary nodule is found, it is. to be regarded as highly probable that the animal bitten was not mad. Peri cellular nodules speak in favor of rabies. When the medulla. spinal cord, and ganglia present no leucocytic thromboses or perivascular or pericellular undula tions, it is very probable that the (log was not mad, and, if the animal died a. natural death besides, rabies was cer tainly not present. V. Babils (La Presse MOd., Sept. 8, 1000).
Etiology.—It attacks by preference the carnivora and in particular the dog and allied species. although human be ings, cattle, horses, and swine are occa sionally infected. It is transmitted from one animal to another by inoculation, usually from a bite, and is comparatively rare in countries and localities in which the muzzling of dogs is made compul sory.
In the dog the first symptoms appear from a few days to weeks after infection. The animal shows a change in disposi tion, becoming unusually irritable and snappish, although when left alone seem ing dull and somnolent. Food is often refused and the animal eats or chews sticks, dirt, leaves, straw, etc. The dog becomes weak, tremulous, and unsteady on its legs in the paralytic or more com mon form, but in the "furious" form of the disease there is wild excitement, the animal running aimlessly about, bark ing, growling, and snapping at or biting anything in its way. In either case the creature soon becomes helpless, coma tose, and dies. The toxic principle of rabies is widely diffused throughout the bodily tissues, and the disease has been produced by the experimental inocula tion of portions of the nervous organs, salivary and mammary glands, suprar enal bodies, and pancreas. The virus is
almost surely the product of a specific micro-organism, although bacteriologists have thus far been unsuccessful in at tempts to isolate the pathogenic germ.
The essential cause of hydrophobia is a specific virus, which can only be re produced within the living organism. As a small quantity of this virus intro duced into the tissues can result in the most serious consequences, there exists no doubt that it possesses the properties pertaining to living organ isms, more especially the capacity of re production after its entrance into the body. That the disease is not caused by preformed ptomaines communicated from the saliva of rabid animals is shown by the variable and, on the whole, long stage of incubation which precedes all true infective processes. Another convincing proof of its microbic origin is the well-established fact that the dis ease can be artificially produced by im planting fragments of brain- or cord tissue, taken from animals dead of rabies, into healthy animals. Senn of Slug.," p. 40G, '90).
Rabies is believed to be due to pro tozoa. The parasites only multiply in the nervous tissues and cannot be culti vated. In the living organism the viru lence of the parasites is not reduced by simultaneous inoculation of virulent micro-organisms. The latter, on the other hand, are retarded in their de velopment. A. Grigo•iew (Centralb. 1. Bakt., Parasit., n. Infekt., Oct. 12, '97).
Hydrophobia may be due either to a poison absorbed or it may be caused by constant direct irritation carried from the seat of the bite to the central nerv ous system, giving rise to hyperemia of nerve-centres, and thus an increased function or abnormal action upon their part, inducing thereby all the symptoms of hydrophobia.
In all nervous forms of disease the main factor inducing the symptoms is active within, and therefore excessive function of, central nerve-cell,. B. O. Kinnear (Medical Record, July 22, '99).
The virus of the dog remains potent for a long time, having been found active in the carcass of a dog which had died of rabies forty-four days before. The period of incubation is between 20 and 60 days, the disease being rare after a longer period. J. H. Brndfors (Lancet, Mar. 3, 1900).