Observations on the Protective Action of Normal Serum. 
293 
Protective Action of the Serum of Different Animals. 
The serum from various animal species (ox, sheep, man, rabbit, cat) was 
found to confer the same protection as horse serum ; in the experiments of 
other workers on this subject the phenomenon has been studied from the 
point of view apparently of its being related to horse serum only ; the effect 
is, however, not characteristic of the serum of only one species of animal 
(Table V). 
The question then arose as to whether the serum of one guinea-pig in- 
jected parenterally into another guinea-pig would protect the latter against 
B. diphtheriae infection. To ascertain this a number of experiments were 
carried out, but with variable results : in some cases complete protection 
was obtained ; in others, while the infected animals succumbed to the dose 
given, there was a distinct delaying of the lethal effect (Table VI). Thus 
it was apparent that though protection by normal serum from an alien 
species was the general rule, the serum of the same species was not without 
a similar effect. 
Table V. 
Guinea-pigs approximately 450 grms. weight injected subcutaneously in 
flank with 3 c.c. of a 2-days bouillon culture of B. diphtheriae, " strain 2 " ; 
serum of various animals injected subcutaneously in back at same time. 
1. B. diphtheriae+10 c.c. ox serum . . . survived. 
2. ,, +10 c.c. sheep's serum . . „ 
3. + 8 c.c. human serum . . ,, 
4. +10 c.c. cat's serum . . 
5. ,, + 6 c.c. rabbit's serum . . ,, 
6. „ +3 c.c. „ „ (55° C.) 
7. ,, +10 c.c. horse serum . . 
8. no serum. .... died 2nd day. 
Table VI. 
Guinea-pigs approximately 400 grms. weight injected subcutaneously 
with 3 c.c. 2-days bouillon culture of B. diphtheriae ; serum from other 
guinea-pigs injected subcutaneously at a different site. 
1. (a) B. diphtheriae, " strain 2 " + 6 c.c. serum . . died 6th day. 
(b) control (no serum injected) . . . • „ 2nd 
2. (a) B. diphtheriae, " strain 2 "+8 c.c. serum (55° C.) . survived. 
(b) control . . . . ■ • • died 2nd day. 
22 
