io8 THOMPSON YATES LABORATORIES REPORT 
No. 4 only differed from the diphtheria bacillus in its slightly less granular 
appearance, and in its non-virulence. It is probably an attenuated diphtheria bacillus 
analagous to that occurring in a throat after an attack of diphtheria, or in the throats 
of apparently healthy children. 
No. 5, although a short variety with few involution forms, produced abundant 
acid in glucose containing media ; it was, moreover, not pathogenic to guinea pigs. 
In addition to the five varieties described in the tabie many intermediate forms 
have been isolated. 
One form with highly segmented protoplasm formed colonies in serum and 
agar indistinguishable from those of the xerosis bacillus, but in litmus glucose broth 
at the end of five or six days acid was produced. 
Another form, also similar to the xerosis bacillus in cultures, was in micro- 
scopical appearance a short oval bacillus closely resembling No. 5 ; it, however, did not 
produce acid in glucose containing media. 
Other forms differing slightly either in morphology or in cultures from one 
or other member described in the table have been noticed, and it would appear 
possible to separate from the eye a complete series of bacilli beginning with the short 
regular form not producing acid in glucose and non-virulent, and ending with a 
typical diphtheria bacillus pathogenic to guinea-pigs. 
Louis Cobbett 1 recognized five types of diphtheria bacilli occurring in the 
throat : — 
1. Oval bacilli with an unstained septum. Young forms 
2. Long, faintly stained, irregularly beaded bacilli 
3. Regularly beaded bacilli. Streptococcal forms 
4. Segmented bacilli 
5. Uniformly stained bacilli 
He found acid-producing bacilli identical in appearance both in culture and 
under the microscope with the diphtheria bacillus which were non-pathogenic. 
Whilst the xerosis bacillus occurred one hundred and twenty times, other 
varieties of the diphtheria group were of comparative rarity in the normal 
conjunctival sac ; in diseased conditions, however, many varieties were often isolated 
from the same eye, Hoffmann's bacillus occurring with almost as much frequency as 
the xerosis bacillus. It is worthy of note that the organism (No. 4) most nearly 
resembling B. diphtheriae was never found in the healthy sac, but was on several 
occasions found in the discharge from catarrhal ophthalmia and other non-diphtheritic 
inflammations. 
1. The result of <)^Q bacteriological examinations for diphtheria bacilli during an outbreak of diphtheria at Cambridge 
and Chesterton. Jr.irnal of Hygiene, vol. i, No. 2. 
