H. Baton 
143 
Exp. 21. Same rat as in Exps. Nos. 8-10 in the previous table ; had therefore 
been unsuccessfully inoculated three times with relapsing fever blood. 14th Dec. 
1910. Inti’a-pei’itoneal injection of 0-.3 c.c. relapsing fever serum containing 
numerous spirochaetes. 
15th Dec. 1910. Numerous “circular” forms seen. 
16th Dec. 1910. Spirochaetes still numerous. 
Next day negative. 
Exp. 22. Same rat as in Exp. No. 11 ; it had therefore been fruitles.sly injected 
once with relapsing fever blood and once with blood from a mouse containing 
numerous spirochaetes. 
14th Dec. 1910. Intra-peritoneal injection of 0’3 c.c. of deiibrinated relap.sing 
fever blood. 
A few spirochaetes were seen next day, but had disappeared 24 hours after. 
Exp. 23. Same mouse as in Exp. No. 1.3. 14th Dec. 1910. Intra-peritoneal 
injection of 0'3 c.c. defibrinated relapsing fever blood in I’S c.c. saline. 
Si^irochaetes detected next and following day. 
Exp. 24. Same mouse as in Exp. No. 14. 14th Dec. 1910. Intra-peritoneal 
injection of 0'3 c.c. defibrinated relapsing fever blood in 0‘5 c.c. saline. 
15th Dec. 1910. Numerous winding circular forms present. 
16th Nov. 1910. Negative. 
Exp. 25. Same mouse as in Exp. No. 15. 14th Dec. 1910. Intra-peritoneal 
injection of 0‘3 c.c. of defibrinated relapsing fever blood in 0‘5 c.c. saline. 
15th Dec. 1910. Spirochaetes with peculiar, lashing, trypanosome-like move¬ 
ments. 
16th Dec. 1910. Negative. 
Marked natural immunity was therefore not present in these animals, 
and the previous unsuccessful attempts may well have been due to the 
strains injected being less virulent than the later ones. 
The blood injected on the 14th Dec. 1910 was the most infective 
of all. It came from a patient who died the next day. He had 
spirochaetes in his blood during nine days and suffered from marked 
icterus ; his temperature, however, did not rise above .39° C. The blood 
contained about 10 to 15 spirochaetes in every oil immersion field. 
Ill. Eocperiments in which infection followed the first inoculation. 
Exp. 26. 18th Nov. 1910. White rat injected intra-peritoneally with 1‘5 c.c. 
defibrinated relapsing fever blood. 
19th Nov. 1910. Spirochaetes numerous. 
Examined with negative results on the 20th, 22nd, 24th, 26th, 27th and 29th 
Nov. 1910. 
Exps. 27, 28. 19th Nov. 1910. Two mice ; intra-peritoneal injection of 0'5 c.c. 
defibrinated relapsing fever blood, which had been kept 24 hours in the ice-chest. 
20th Nov. 1910. Spirochaetes found in both animals. 
