1906.] Main Source of " Precipitable' " Substance, etc. 305 



is not appreciably used up as a result of interaction with precipitin antisera. 

 Yet we have no conclusive evidence that it is so used up, and we have 

 definite evidence that it is not entirely removed by any number of inter- 

 actions or amounts of precipitin antiserum with which it has been tested. 



Experiment V. First Interaction. — To 0"5 c.c. of 1-per-cent. fresh egg 

 white in salt solution (equivalent to 0'0006 gramme dried) there was added 

 4 - 5c.c. salt solution, and then - 01 gramme dried antiserum (prepared in a rabbit 

 by repeated injections of fluid egg white) in 0'2 c.c. saline. After 48 hours 

 there was a deposit measuring between U"5 mm. and 1 mm., and some flocculi 

 in suspension. 



Second Interaction. — The superfluid was then filtered, and to 4 c.c. of the 

 filtrate was again added O'O.l gramme antiserum in 0"2 c.c. saline. In 

 48 hours the precipitate again exceeded - 5 mm., and there was also some 

 suspended matter. 



Third Interaction. — The process was repeated, and 3 c.c. of filtrate plus 

 0*01 gramme antiserum yielded a precipitate about 1 mm. in 48 hours. 



Fourth Interaction. — 2 - 5 c.c. filtrate plus - 01 gramme antiserum gave in 

 48 hours a large precipitate of 2 - 5 mm. 



Fifth Interaction. — 1*5 c.c. filtrate plus 001 gramme antiserum gave in 

 72 hours a 2 -mm. precipitate. 



Sixth Interaction. — The filtrate, measuring 1 c.c, was now divided equally 

 between two tubes, A and B. To tube A was added 04 c.c. of 1-per-cent. 

 fresh egg white in salt solution (0"00012 gramme dried), to tube B 

 0'01 gramme antiserum as before. After 48 hours the precipitates read in 

 tube A - 5 mm., in tube B 2 mm. 



The first four interactions took place in tubes of about 5 mm. diameter, the 

 others in tubes of 4 mm. diameter. 



The smaller precipitates in the earlier interactions were probably due 

 partly to the longer column of fluid through which they had to settle, and 

 partly to the greater dilution of the precipitin antiserum retarding the 

 reaction and rendering it not quite complete even in 48 hours. 



The fluids did not altogether escape bacterial contamination, but up to the 

 final interaction there was never more than a faint cloud beneath the aerial 

 surface of the fluid. There was never any surface scum or pellicle, or any 

 bacterial clouding in the deeper parts of the tube. The precipitates were 

 distinctly flocculent, and could not have been mistaken for bacterial deposits. 

 These remarks also apply to the other exhaustion experiments to be latei 

 described. 



Notwithstanding, therefore, the progressive diminution of the available 

 homologous proteid at each stage and the successive addiments of antiserum, 



VOL. LXXVIII. — B. 2 A 



