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been observed in a fully virulent condition. Thus Aaser' found the diphtheria bacillus present in. 17 out of 895 soldiers in a cavalry regiment. Park and Beebe found that of 330 persons examined at random, 8 had fully virulent bacilli and 24 characteristic but nonvirulent bacilli in their throats. Meade Bolton, among 214 persons more or less exposed to the disease, found virulent bacilli present in 41.5 per cent., and the literature teems with similar cases.

It by no means follows that all the persons in whose throats the diphtheria bacilli are found are suffering at that moment from clinical diphtheria. In a large school of 800 children during an epidemic of sore throat and clinical diphtheria 4 I found 33 per cent. of the whole school bad characteristic bacilli present in their throats, while only 14 out of the total number of children examined showed clinical symptoms of the disease. In three of the cases in which no clinical symptoms had at any time manifested themselves, the organisms were in a fully virulent condition, causing the death of injected guinea-pigs, in forty-eight hours, with all the characters of infection with the diphtheria bacilli. The importance of those @co-parasites lies in the ease with which they may be transferred from one mouth to another until a susceptible individual becomes the recipient, when grave, often fatal, disease may result; it is, moreover, these“ bacillusträgende " persons who may come under the care of the dental surgeon and form an unrecognised centre of infection.

Occurrence.—The Klebs-Læffler bacilli are found most frequently upon the throats of persons suffering from faucial diphtheria, but are also found occasionally in open wounds, causing wound diphtheria, and upon the conjunctiva.

The bacilli have also been found in milk, wbich is an excellent medium for their development, several epidemics having been traced to contamination of the milk supply from infected persons.

The organisms rapidly die wben introduced into water, and they have never been found in samples of water submitted to examination, nor have they been found in sewage, or in drain and sewer air, or in the emanations of decomposing animal or vegetable matter.

The bacilli will withstand drying for several weeks, and may undoubtedly remain in the dust of rooms in a virulent condition..

"Deutsch. Med. Woch., 1895, p. 357. ? New York Med. Record, xlvi., 1894.

3 Med. and Surg. Reporter, lxxiv., p. 799.
+ Trans. Epidem., 1900, p. 99.

They are easily destroyed by the action of germicides, and by a temperature of 58° C. for ten minutes.

When grown in a current of air, Fernbach found that the growth was more luxuriant, but the life cycle shortened. The organism will also grow when air is entirely excluded, and is therefore äerobic and facultative anäerobic. The bacilli may be cultivated upon the ordinary laboratory media, but are morphologically most typical upon coagulated blood serum, the medium largely used for diagnosis.

Leffler's blood serum gives even better results; this medium consists of blood serum (liquid) 3 parts, glucose (1 per cent.) broth 1 part.

Coagulation and sterilization are carried out as for ordinary blood serum.

Diagnosis.-In the routine examination of suspected throats for diphtheria bacilli, now largely carried out at the public expense in most British towns, a “ sterilized swab ” (consisting of a wire, the end of which is wrapped round with cotton wool, and kept till use in a sterilized and cotton wool plugged tube) is introduced into the throat and the surface touched with the sterile wool of the swab. Blood serum tubes are then inoculated, incubated and the culture examined in eighteen to twenty-four hours, when the typical bacilli are sought for. If diphtheria bacilli be present, the colonies, at the end of twenty-four hours will be larger and more defined than those of other bacteria present.

Ohlmacher recommends the examination of the culture in five hours, even though no growth be visible, but a negative result by this means would hardly be of sufficient value to obviate a further examination at twenty-four hours; still a positive result obtained at this time (five hours) is certainly of value. Equally good results may be obtained by examining coverslip preparations of the throat membrane direct and by this method the cultural diagnosis may be forestalled in about 30 per cent. of cases, the stain used being Neisser's two solutions.

Varieties.-Two distinct varieties of the diphtheria bacillus are known, one the short variety, usually considered the least pathogenic, and the “ long variety” or most virulent; the ends of the long variety are more frequently swollen and clubbed than the short variety. Both varieties form very short rods upon agar, whilst upon blood serum the “long” variety grows out into rods of 5 to 8 u in length, or even longer.

[graphic][subsumed]

Fig. 39.- DIPHTHERIA BACILLUS. Twenty-four hours' agar cultivation. Stained Gram. Washbourn and Goodall's “Infectious Diseases.").

[graphic]

Fig. 40.- BacilLUS DIPHTHERIÆ. Forty-eight hours' blood serum cultivation. Stained Gram.

* 1000. (From

x 1000.

Morphology.—Straight and slightly curved rods 3 to 4 u long (twenty-four hours blood serum cultivation), often showing segmentation of the cell plasm by which the bacilli stain irregularly, especially with methylene blue.

By Neisser's method these bands are stained as blue dots, the rest of the organism brown. The bacillus usually lie grouped together with their long axes parallel, constantly the bacilli are of tapering wedge-shaped form, with the bases in apposition.

In older cultivations the ends of the bacilli become swollen and club shaped, forming the characteristic form. Various involution forms occur, the organisms becoming very much swollen, wedge shape, ovoid, &c. The segmentation of the cell plasm is usually well marked. In these older cultures red granules are often to be seen in specimens stained with carbol methylene blue. The organism retains the stain of Gram's method.

Various branched forms have been observed in old cultures as has been also observed with the tubercle bacillus, it is therefore suggested by Hueppe and others that these two organisms are really only a phase in the life cycle of some higher organism allied to the Streptotricheæ, such as S. actinomyces. Chester calls them myco-bacteria.

The diphtheria bacillus is not known to produce spores, although the condensation of the protoplasm and plasmolysis often gives the appearance of sporulation; still the death of the organism at the low temperature of 58° C. precludes the presence of true endogenous spores.

The diphtheria bacillus is not motile and is not known to possess flagella.

Biology.-Growth occurs on the ordinary laboratory media at 37.5° C., and at 22°, the optimum temperature being that of the body. The organism is facultative anäerobic and does not liquefy gelatin, and produces no pigment.

Gelatin Streak, 22° C.-In three days small discrete, raised white colonies, or confluent streak, edge indentate, no liquefaction.

Gelatin Stab, 22° C.-Minute granular, discrete colonies to bottom of stab, no liquefaction.

Gelatin Plates, 22° C.-Minute wbite points, granular, irregular, under the z" granular, irregular and yellowish-brown.

Agar Streak, 37.5° C.-In twenty-four hours does not grow luxuriantly at first, but does so after several transplantations.

Glycerine Agar, 37.5o C.--Delicate moist white to yellowish. Colonies.-Macroscopical (a) Superficial, delicate, grey-white,

translucent. (6) Deep, oval, grey, entire, amor

phous. Microscopical (a) Superficial, round, entire, yel

lowish, translucent. Blood Serum, 37.5° C.-Opaque wbite or grey raised colonies, or dull granular moist grey streak.

Potato, 22° C.-Glistening growth on alkaline potatoes which has the same colour as the medium. No growth on acid potato.

Litmus Milk, 37.5° C.-Twenty-four to forty-eight hours acid, no coagulation, later an alkaline reaction appears.

Broth, 27-5° C.-Twenty-four hours granular deposit with fine flocculi, often forming a surface film. Reaction at first acid, later alkaline.

Glucose Broth, 37.5o C.-Acid production. Acid is also formed from glycerine.

Peptone Water, 37.5o C.-Indol produced in seven days. In old cultures some nitrite is also formed, so that a cholera red reaction is given with pure sulphuric acid (nitrate free). A slight amount of sulphuretted hydrogen may be produced.

Pathogenesis. — Inoculation of animals by the subcutaneous method with small quantities of the diphtheria bacilli causes death in from three to six days. Guinea-pigs are the most susceptible, rabbits being considerably more resistant. Subcutaneous inoculation of guinea-pigs with 0.1 to 0.3 cubic centimetres of broth culture results in death. The pathological changes observed at the autopsy are extensive ecchymosis and local ædema at the seat of inoculation, increase of fluid in the various serous cavities, pericardial, pleural and peritoneal; injected, enlarged and hæmorrhagic suprarenal capsules, with occasionally a slight swelling of liver and spleen. There may be a good deal of lymphatic enlargement and congestion, but it is not a constant symptom. Small dotted areas of necrosis and fatty degeneration are often found in the liver, kidney, and heart muscle, more particularly in those cases in which death is long delayed. The most typical lesions are the fibrous-gelatinous exudation at the seat of inoculation from which the diphtheria bacillus can be recovered in pure culture, and the hæmorrhagic suprarenal bodies.

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