220 BACTERIA PATHOGENIC TO MAN 



and cocci, and in others a great excess of cocci. Besides these, there 

 will be occasionally met preparations in which, with the cocci, there 

 are mingled bacilli more or less resembling the Loeffler bacilli. These 

 bacilli, which are usually of the pseudodiphtheria type of bacilli (see 

 Fig. 63), are especially frequent in cultures from the nose. 



In not more than one case in twenty will there be any serious difficulty 

 in making the diagnosis, if the serum in the tube was moist and had 

 been properly inoculated. In such a case another culture must be 

 made or the bacilli plated out and tested in pure culture. 



Direct Microscopic Examination of the Exudate. An immediate 

 diagnosis without the use of cultures is often possible from a micro- 

 scopic examination of the exudate. This is made by smearing a 

 slide or cover-glass with a little of the exudate from the swab, drying, 

 heating, staining, and examining it microscopically. This examination, 

 however, is much more difficult, and the results are more uncertain 

 than when the covers are prepared from cultures. The bacilli from 

 the membrane are usually less typical in appearance than those found 

 in cultures, and they are mixed with fibrin, pus, and epithelial cells. 

 They may also be very few in number in the parts reached by the swab, 

 or bacilli may be met with which closely resemble the Loeffler bacilli in 

 appearance, but which differ greatly in growth and in other charac- 

 teristics, and have absolutely no connection with them. When in a 

 smear containing mostly cocci a few of these doubtful bacilli are present, 

 it is impossible either to exclude or to make the diagnosis of diphtheria 

 with certainty. Although in some cases this immediate examination 

 may be of the greatest value, it is not a method suitable for general 

 use, and should always be controlled by cultures. 



When carried out in the best manner an experienced bacteriologist 

 may obtain remarkably accurate results. Higley in New York in a 

 series of consecutive throat cases made the same diagnosis from the 

 direct examination of smears as the Health Department laboratory 

 made from the culture. To get the exudate he used a probe armed 

 with a loop of heavy copper wire which has been so flattened as to 

 act as a blunt curette. He makes thus thin smears from the exudate. 

 After drying and fixing by heat the smears are stained for five seconds 

 in a solution made by adding five drops of Kiihnes carbolic methylene 

 blue in 7 c.c. of tap-water. After washing and drying stain for one 

 minute in a solution of 10 drops of carbol-fuchsin in 7 c.c. of 

 water. The dilute solution should be freely prepared. The diphtheria 

 bacilli will appear as dark-red or violet rods, and their contour, 

 mode of division, and arrangement are manifest. 



Animal Inoculation as a Test of Virulence. If the determination of 

 the virulence of the bacilli found is of importance, animal inoculations 

 must be made. Experiments on animals form the only method of 

 determining with certainty the virulence of the diphtheria bacillus. 

 For this purpose, alkaline broth cultures of forty-eight hours' growth 

 should be used for the subcutaneous inoculation of guinea-pigs. The 

 amount injected should not be more than one-fifth per cent, of the body- 



