Observations on the Protective Action of Normal Serum. 
291 
Minimum Lethal Dose Estimation. 
Guinea-pigs approximately 400 grms. weight 
subcutaneously. 
B. diphtheriae bouillon culture, 1-5 c.c. 
1-0 c.c. 
0-5 c.c. 
0-25 c.c. 
0-1 c.c. 
0-05 c.c. 
same culture injected 
died 2nd day. 
„ 2nd „ 
„ 4th „ 
„ 7th „ 
survived. 
Prophylactic as opposed to Curative Effect. 
It was found that normal serum, though protective or prophylactic, was 
not curative ; thus, to elicit the antagonistic effect, the serum had to be 
injected without delay after the introduction of the infecting organisms ; 
if an interval of two hours or longer was allowed to elapse before the serum 
was injected, even when five times the protective dose was used, the animals 
died (Table II). 
Thermostability of the Active Substance in the Serum. 
In thermostability the active principle of the serum corresponds gener- 
ally to antitoxin and other antibodies. Horse serum heated for one hour 
at 57° C. was still protective, but was inactivated by exposure at 70° C. 
for half an hour and at higher temperatures (Table III). The thermo- 
stability at 57° C. excluded the possibility of the active substance being of 
complement nature. 
Table II. 
Guinea-pigs approximately 400 grms. weight injected subcutaneously 
in flank with 3 c.c. 2-days bouillon culture of B. diphtheriae, " strain 3 " ; 
10 c.c. normal horse serum injected subcutaneously in back at varying 
intervals after injection of the culture. 
1. B. diphtheriae-h serum, simultaneously . . survived. 
2. 
3. 
4. 
5. 
+ 
+ 
after 2 hours 
» 4 
„ 24 „ 
no serum . 
died 3rd day. 
2nd „ 
„ 2nd „ 
2nd „ 
Table III. 
Guinea-pigs approximately 450 grms. weight injected subcutaneously 
flank with 3 c.c. of a 2-days bouillon culture of B. diphtheriae, 
