64 
contents flowed back into the barrel of the syringe, owing to accidental 
withdrawal of the piston. This particular guinea pig showed no 
symptoms as a result of the injection; whereas we knew it to be sus- 
ceptible, because a subsequent operation, done a few hours later, 
caused characteristic symptoms. 
For intraperitoneal inoculations the needle should be short and 
blunt to avoid this accident and the injection should be given over 
the region where the coils of small intestine lie close to the abdominal 
walls. 
NEUTRALIZING EFFECT OF THE BLOOD AND ORGANS OF AN IMMUNIZED GUINEA 
PIG UPON THE TOXICITY OF HORSE SERUM. 
We found that repeated injections of horse serum into a guinea pig 
produces a certain degree of immunity to the subsequent action of 
horse serum, and it naturally occurred to us to try whether such 
guinea pigs contained in their body juices an immunizing substance 
in sufficient quantity to neutralize the poisonous substance found in 
horse serum. 
G. P. No. 109 (immunized) . This guinea pig had received 10 subcutaneous inoculations of 
1 c. c. each of antitoxic horse serum (Natl. IX. 19) on 10 successive days from Feb. 8 to 20; 
15 days later, viz, March 7, it was inoculated with 6 c. c. antitoxic horse serum (Natl. IX. 
19) into the peritoneal cavity. No symptoms. 
Twenty-one days later, viz, March 28, it was again tested by injecting 6 c. c. of antitoxic 
horse serum (Natl. VIII. 18) into the peritoneal cavity. No symptoms. 
As this guinea pig showed a high degree of resistance to the toxic action of horse serum 
it was killed two days later, March 30, with chloroform. About 15 c. c. of the blood was 
taken from the heart and defibrinated, the various organs were removed and placed in 
separate mortars and ground up with 10 c. c. of antitoxic horse serum (Natl. VIII. 18). 
This mixture of horse blood with organ juices of the guinea pig was allowed to stand about 
3 hours at room temperature and strained through cheese cloth. It was then inoculated 
into the guinea pig. 
G. P. No. 166. Six c. c. antitoxic horse serum (Natl. VIII. 18) mixed with suprarenal of 
g. p. 109 injected into the peritoneal cavity. Dead in 9 minutes. 
[Previous treatment: 49 days prior, inoculated with 0.22 c. c. toxine No. 7+3inr c - c - 
horse serum (Stearns No. 1351).] 
G. P. No. 158. Six c. c. same serum as g. p. 166 mixed with whole (defibrinated) blood of 
g. p. 109 injected into peritoneal cavity. Dead in 15 minutes. 
[Previous treatment : As g. p. 166.] 
G. P. No. 126. Six c. c. same serum as g. p. 166 mixed with thyroid of g. p. 109 injected into 
peritoneal cavity. Dead in 16 minutes. 
[Previous treatment: As g. p. 166.] 
G. P. No. 132. Six c. c. same serum as g. p. 166 mixed with Tddney of g. p. 109 injected into 
peritoneal cavity. Symptoms, recovered. 
[Previous treatment: As g. p. 166.] 
G. P. No. 164. Six c. c. same serum as g. p. 166 mixed with spleen of g. p. 109 injected into 
peritoneal cavity. Symptoms, recovered. 
[Previous treatment: As g. p. 166.] 
