Pathology and Etiology. Sir James Simpson suggested in 1854 that puerperal and surgical tetanus was due to the absorption of a poison produced in the wound (Woodhead). Spinola charged it on infection in wounds in horses. Carle and Rattone in 1884 successfully inoculated 11 out of 12 rabbits with the products from the wound of a man suffering from tetanus. A year later Nicolaier produced tetanus in animals by inoculating them subcutem with garden mould or street dust, and found in the suppurating wounds in connection with various other microbes a minute bacillus longer but thinner than that of mouse septicæmia to which he attributed the tetanizing action. In 1886 Rosenbach inoculated two Guinea pigs with the pus of a tetanic man, and found in the sores of the tetanic pigs the bacillus of Nicolaier in company with another larger spore-forming bacillus. In 1889 Kitasato succeeded in making pure cultures of the bacillus tetani, and successfully inoculated the disease on mice, rabbits, and Guinea pigs producing typical tetanic symptoms and death. This was promptly corroborated by Tizzoni and Cattani and later by a great variety of observers.
Bacillus Tetani. This organism is a minute rod 4 to 5μ in length by 0.2 to 0.3μ in thickness, with slightly rounded ends. In many mature forms the one end is enlarged by the formation of a spherical, refrangent spore which gives the bacillus the appearance of a pin or a “drum-stick.”
The bacillus is anærobic, liquefying, tardily motile, and sporogenous. When spores form the bacillus loses its motility. It grows at room temperatures, in ordinary culture media which have a feebly alkaline reaction, and in an atmosphere of hydrogen, but more actively at a temperature of 36° to 38° C. Below 14° C. growth ceases and the bacillus is killed at 60° to 65° C. The spores, however, can resist a temperature of 80° C., in water for an hour, and 100° C. for four minutes. It was this unusual resistance of the spore to heat that enabled Kitasato to kill off the contaminating organisms and obtain pure cultures from the surviving spores. The spores will survive desiccation for years, retaining their virulence, and may live 2½ months in putrefying material. The addition to the culture medium of 1½ to 2 per cent. of glucose makes the growth much more rapid and abundant, and causes opacity in the medium. The upper portion clears up in 6 or 7 days by the precipitation of the bacilli as a grayish mass. In a glucose culture medium growth is not prevented by the presence of oxygen at the surface. The colonies formed in gelatine plate cultures show an opaque centre with fine divergent rays, and a similar radiating growth is shown in deep stick cultures. At the end of the second week the gelatine begins to liquefy and form a little gas, and finally the whole mass becomes soft and sticky. The bacillus does not liquefy blood serum. Cultures have a disagreeable aromatic odor.
The bacilli stain readily in aniline colors and by Gram’s method. The spores may be stained by Ziehl’s method. To 10 parts of a 10 per cent. alcoholic solution of basic fuchsin, add 100 parts of a watery solution of carbolic acid. Float the cover glass upon this, heating gently for three to five minutes until steam begins to rise, wash well in water, and decolorize in nitric or sulphuric acid, 25 per cent. solution, then in 60 per cent. alcohol to remove color from albuminous background. Wash in water and mount. By placing the specimen for two minutes in a watery solution of methylene blue a contrast is obtained, the bacillus blue and the spore red.
Outside the animal body the bacillus has a saprophytic life in rich garden mould, street dust, stables, yards and drains, and the cracks of floors. Nicolaier failed to obtain it in soil from forests and from the deeper layers of garden earth. Marchesi found it to a depth of two metres but no more. Again it is much more abundant in tropical countries than in temperate and cold ones, and appears to be to a great extent limited to particular localities. It has been found in the intestinal contents of man and horse (Babes, Sormani), and in horse manure, and this mingling with the surface soil and generating an abundance of ammonia determines the anærobic conditions which favor the growth of the microbe. This serves to explain the remarkable prevalence of the disease among those living or working about stables, gardeners, agricultural laborers, soldiers on campaign, and children and others walking with bare feet. The contact with rich infected soil greatly favors inoculation in any accidental wound.
An important feature in the pathology of tetanus is that the bacillus is confined to the seat of the inoculation wound. The many attempts to transmit the infection by blood, nervous matter, and by one or other of the tissues have uniformly failed, though the pus of the infected wound has proved virulent. Similarly, the attempts of Kitasato and others to obtain cultures from the animal liquids or tissues apart from the wound have been futile.
By inoculating the toxins remaining in the pus of the infection wound, however, or in virulent cultures from which the bacilli have been removed by filtration or in which they have been destroyed by heat, all the symptoms of tetanus can be produced (Kitasato, Kund Faber, etc.) In such cases too, the symptoms appear at once, as soon as the toxin is absorbed, and not after a definite period of incubation as in inoculation of the unaltered virus. Kitasato, Vaillard and Vincent reached this conclusion by another channel. They inoculated mice at the root of the tail with virulent tetanus cultures, and at definite intervals after, namely, half an hour, one hour, and one and a half hour, they made a circular incision round the wound and thoroughly cauterized the whole, thus destroying all the inoculated bacilli. They found that tetanus was prevented in those animals only which were operated on at the first half hour. Again, Kitasato injected mice with 0.2 to 0.3cc. of the blood from the heart of a fresh tetanus cadaver, and thereby produced typical tetanic symptoms and death in 1 to 3 days.
Various poisons have been separated from cultures of bacillus tetani. Brieger isolated three substances—tetanin, tetano-toxin and spasmotoxin—which in large doses caused tetanic symptoms and even death. Brieger and Fränkel later isolated a toxalbumin which proved of incomparably greater potency. Again, Brieger, Kitasato and Wehl separated what appeared to be an enzyme or diastase which proved 500 times more potent than atropia. This was in the form of yellow, transparent flakes, soluble in water, but which was not destroyed by drying, nor in the dry state by absolute alcohol, chloroform nor anhydrous ether, but which, like the virulent cultures of tetanus, was easily destroyed by acids, alkalies, hydrogen sulphide, or heat. Like the natural virulent product this may be kept unchanged for months on ice, apart from the light, or with the addition of 0.5 per cent. of carbolic acid, or its own bulk of glycerine. It kills the Guinea-pig in a dose of 0.000025 gramme, and the mouse in a dose of 0.00000025 gramme.
While the propagation of the bacillus in the animal body appears to be local, and the general tetanic symptoms are caused by the absorption of the poison, it remains to be seen on what organ this directly operates, and what accessory conditions favor its efficiency.
In cases due to inoculation the spasms are at first local in the vicinity of the inoculation wound and later become general. Kund Faber shows that there is no gradual transition from the local manifestations to the general, but the latter appear abruptly and in force as a new and independent phenomenon. When we consider further that in inoculation with pure cultures (uncontamininated by pus or saprophytic microbes) the wound often heals promptly, without any sign of remaining local irritation, we may conclude that simple nervous irritation in the sore cannot be invoked as a cause of the early local spasm. It is more likely due to the local diffusion of the poison into the peripheral nerves while the little that has been absorbed is as yet too much diluted in lymph and blood to seriously derange the nerve centres.