42 



equivalent of 0-2 c.c. of serum is contained in 0*5 c.c; it has 

 a found, however, that dilution to 1 in 5 does not affect the 

 protective power of a serum. 



The amount of absorbing culture used cannot exceed a certain 

 limit: in some of the absorption experiments, the amount of 

 thick culture emulsion added to pure serum was such that, 

 after prolonged centrifuging, only a third of the original serum 

 could be recovered. 



Some examples of absorption experiments with Group IV 

 sera will be given in the case of Pn. 10, the serum of which was 

 strongly protective and agglutinating, while the cultures of 

 Pn. 10 and Pn. 30 of the same type were highly virulent. 



Experiment 1. — Pn. 10 serum was absorbed with Pn. 30 culture, which 

 was not the homologous strain but was of the same type. The test of 

 protection was also made with Pn. 30 culture. Before absorption, the 

 serum inoculated in doses ranging from 0-2 c.c. to 0-05 c.c, protected 

 mice against 0-1 c.c. of broth culture of the test strain, Pn. 30; 0-01 c.c. 

 of serum was ineffective. After absorption, which consisted in treatment 

 of 1 • 5 c.c. of serum with the deposit of 800 c.c. of broth culture on two 

 successive occasions, the final dilution of serum being 1 in 5, there was 

 some diminution in protective power but not complete exhaustion. The 

 serum in doses of 0-2 c.c. still protected mice against 0-01 c.c. of broth 

 culture but failed against 0- 1 c.c. 



Experiment 2. — To 1 c.c. of Pn. 10 serum was added the deposit of 

 400 c.c. of broth culture of Pn. 30, the final concentration of serum in the 

 mixture being 1 in 5. After standing overnight in the ice-chest, the 

 mixture was centrifuged. As before, the unabsorbed serum in doses of 

 • 2 c.c. protected mice against • 1 c.c. of broth culture of the absorbing 

 -train Pn. 30. After absorption 0-2 c.c. of serum protected against 

 0-001 c.c. but not against 0-01 c.c. In this instance removal of the pro- 

 tective bodies was more complete than in the first experiment. 



Experiment 3. — Absorption of Pn. 10 serum with the homologous 

 strain and test of protection versus Pn. 30 culture. Two cubic centi- 

 metres of serum were treated with the deposit of 300 c.c. of broth culture 

 contained in 8 c.c. of uncentrifuged broth culture. The culture was added 

 to the serum on two separate occasions and the mixture, in which the serum 

 was diluted 1 in 10, was centrifuged after standing overnight in the ice- 

 chest. The unabsorbed serum (0-2 c.c. in 2 c.c.) protected mice against 

 0- 1 c.c. of culture. After absorption 0*2 c.c. failed to protect mice against 

 0-000 001 c.c. of broth culture. Thus almost complete exhaustion was 

 effected. 



The above experiments show that Pn. 10 serum was not 

 readily exhausted of its protective substances. On the other 

 hand a single treatment of 1*5 c.c. of Type I or Type II serum 

 in a concentration of 1 in 5 with the deposit of 400 c.c. of broth 

 culture resulted in effective absorption. 



Experiment 4.— Another Group IV. serum, Pn. 26, was absorbed with 

 a suspension of the homologous strain. To 2 c.c. of serum were added 2 c.c. 

 of culture emulsion, after an interval, a second 2 c.c, then 1 c.c. ; after 

 standing overnight in the ice-chest the mixture was centrifuged and 4*5 c.c. 

 of clear supernatant fluid were recovered out of 7 c.c, the remainder con- 

 sisting of deposited culture. A further quantity of culture was added to 

 the recovered dilution, which after a few hours was centrifuged clear. 

 The absorbed serum was tested for protective power versus a culture of 

 the same type which killed mice in doses of 0-000 000 01 c.c. of broth. It 

 was found still to protect against 0-000 001 c.c but failed against 

 0-000 1 c.c and higher doses. 



