296 
Transactions of the Royal Society of South Africa. 
1. Toxin O-OOl c.c. + 10 c.c. serum 
died 2nd day 
„ 2nd „ 
survived. 
2. „ 0-0001 c.c.+ 
3. „ 0-00005 c.c.-f 
4. „ 0-00001 c.c.+ 
Lethal Dose Estimation. 
1. Toxin 0-001 c.c. . . . died 2nd day. 
2. „ 0-0001 c.c. . 2nd „ 
3. „ 0-00005 c.c. . . . survived. 
4. „ 0-00001 c.c. . 
The Occurrence of Local Lesions in Animals surviving after 
Protection by Serum. 
An interesting feature of these experiments was the occurrence of a 
marked local lesion in animals surviving after protection by normal serum 
against B. diphtheriae or its toxin. 
After two to three days a well-marked subcutaneous indurated swelling 
with surrounding inflammatory oedema developed at the site of injection 
of the organisms or toxin ; the overlying skin then became necrotic and 
sloughed, leaving a punched-out ulcer with a grey sloughing base ; the 
lesion attained its full development in eight to ten days, and then slowly 
healed ; in one instance the lesion involved the deeper tissues, and led to 
perforation of the whole abdominal wall. 
It was found that diphtheria antitoxin prevented the occurrence of the 
local lesion as well as the general effects. 
This type of lesion occurred in rabbits protected by serum as well as 
in the case of guinea-pigs. 
In the infection experiments no diphtheria bacilli could be detected in 
the ulcers after sloughing of the skin, either by microscopic examination or 
culture. On the other hand, in experiments where the injection of guinea- 
pig serum delayed the lethal effect of B. diphtheriae for several days (e.g. 
eight days, nineteen days, v. Table VI), and similar sloughing ulcers de- 
veloped at the site of inoculation, B. diphtheriae were present in the lesion. 
Thus the parenteral injection of normal serum, though protecting against 
the lethal result of infection with B. diphtheriae, had no influence on its 
local toxic action. It was apparent also that B. diphtheriae did not persist 
in the tissues of animals fully protected by serum. 
In unprotected animals the local lesion of the type described is not 
commonly met with, as animals infected with a sufficient dose die within 
a few days ; for the full development of the local effect a period of eight to 
