The best culture-medium for routine work is the Loeffler blood-serum, coag ulated by heat in test-tubes in such a way as to give an extensive slanting sur face for inoculation. The swabs used in obtaining the infected material from the throat are made by wrapping a small quantity of absorbent cotton about the end of a small steel rod- six inches in length. The swabs so made are inserted into test-tubes, which are then plugged with cotton and the whole sterilized by exposure to dry heat at 150° C. for one hour. To make a satisfactory culture a good view of the throat must be ob tained and the swab rubbed upon the surface covered by membrane, or—in the absence of membrane—upon the in flamed parts. In laryngeal cases where no membrane is visible it usually suffices to make the application of the swab either to the tonsils or as low in the pharynx as possible. In such cases if the first culture fail to show the pres ence of diphtheria bacilli, it is always well to repeat the process, as a second or third culture may show the bacilli pre viously absent from the accessible parts of the throat. Care must be taken in inoculating the swab not to allow it to touch the tongue or any other part or surface than the one upon. which the presence of the bacilli is suspected. Otherwise contaminating bacteria are in oculated upon the culture-media and the value of the culture for diagnostic pur poses destroyed.
To carry out these directions in young children it is necessary that they be care fully held. The best method is to have the mother or nurse hold the child upon her right side, the child's face turned toward the light and the head resting upon her right shoulder, one of the hold er's arms about the patient's legs, the other controlling the arms. The physi cian can then usually insert a tongue depressor and control the head with one hand, while with the other the swab can be properly directed. With very fractious children it may even be necessary to have a second assistant hold the child's head. Failure to take pains in making a proper application of the swab is accountable for many of the unsatisfactory results ob tained from cultures. The swab having been properly inoculated, the cotton stopper is withdrawn from the mouth of the tube containing the solidified blood serum and the swab then rubbed gently over the surface of the culture-medium, care being taken not to break the smooth surface of the medium. The swab is then withdrawn, the cotton stopper, which must have been held so as to have escaped contamination from any outside source, replaced in the mouth of the culture-tube, the swab dropped into its tube again and confined by its own stop per. The culture-tubes are then ready for incubation. Koplik has described a rapid method of incubation and examina tion in which he allows only two or three hours' incubation at 37° C., at the end
of which time he asserts that the growth of the diphtheria bacilli is more charac teristic than at any other period of in cubation.
There is no positive criterion by which the true diphtheria bacillus can be rec ognized in culture after twenty-four hours. The pscudodiphtheria bacillus is, culturally, practically indistinguishable from it, differing only in its lack of virulence. Hoffman considers the pseudo diphtheria bacillus a constant inhabit ant of the mouth. Roux and Yersin found it twenty-six times in fifty-nine children of a village on the coast of France in which diphtheria was entirely absent. Hoch discovered it twenty-six times in sixty-six- healthy children. In view of this, what value can a method possess by which, in the required time of twenty-four hours, it is impossible to distinguish tbe true diphtheria bacillus from a constant inhabitant of the mouth? The length of the bacilli has been fre quently regarded a characteristic feat ure, but very long bacilli with all the qualities of the Loeffler bacilli, except that they were non-virulent, were found in the conjunctival sac. The true diph theria bacillus in culture, especially on white of egg, exhibits a sort of giant growth, and presents true branching, a phenomenon also observed in the growth of the conjunctival bacillus. In view of all these facts, it is plainly not pos sible to distinguish the virulent from tbe non-virulent bacillus, and too much importance should not attach to bacterio logical diagnosis without determination of virulence, especially when tbe diag nosis is made within twenty-four hours. Schanz (Berl. klin. Woch., Jan. 18, '97).
The advantages of ox-serum as a cult ure-medium for the diphtheria bacillus are that the true bacillus can be easily distinguished from the bacillus of Hoff man, as the colonies of the former are flat, almost colorless, and indented at the edge somewhat like a daisy, while the colonies of the bacillus of Hoffman are elevated, brilliant white, do not adhere to the surface, and give no opalescence in the medium. However, it takes sev eral days to get a characteristic culture, while with horse-serum culture is ob tained within six or eight hours. L. Cobbett (Lancet, Feb. 5, '98).
Upon blood-scrum and agar the xerosis bacillus resembles closely the diphtheria bacillus. It is not pathogenic for ani mals. It grows more abundantly on Loeffler blood-serum and on peptone-agar than the pscudobacillus. Neisser's method of staining decolorizes the xero sis and pseudobacillus, while the diph theria bacillus retains the stain. Bouil lon is rendered acid by the diphtheria bacillus, alkaline by the xerosis bacillus, and it is not affected by the pseudo diphtheria bacillus. E. Franke Pliinch. med. Woch., Apr. 19, '98).