298 
Transactions of the Royal Society of South Africa. 
2. Two c.c. of normal horse serum may protect in this way against 
12 M.L.D. of a B. diphtheriae culture. 
3. No protection occurs if the serum injection is delayed for two hours 
after the inoculation. 
4. The activity of the serum persists at 57° C, but is lost at 70° C. and 
higher temperatures. 
5. The serum of one guinea-pig injected subcutaneously into another is 
either protective to the latter experimentally infected with B. diphtheriae, 
or at least exerts a definite delaying effect on the course of the infection. 
6. Normal horse serum is also similarly protective in guinea-pigs in- 
jected with diphtheria toxin ; 10 c.c. of serum may protect against 10 M.L.D. 
7. The serum of one guinea-pig is not protective in the case of another 
injected with diphtheria toxin. 
8. In the case of animals surviving after protection by normal serum, a 
marked local lesion develops at the site of inoculation. 
REFERENCES. 
Kolle and Schlossberger. — Med. Klinik, 1919 (also quoted by Kraus and Sordelli). 
Kratjs and Sordelli. — Zeit. f. Immunitats., Teil i, Orig. 31, 2, 1921, 107. 
CowiE and Greenthal. — Journ. Med. Research, 1921, 42, 261. 
