PHYSICO-CHEMH.AL PROPERTIES 71 



(1935) deteriorated Avitliin three Aveeks lollowing their prepara- 

 tion. 



It was frecjiiently noticed that the potency of filtrates may also 

 substantially increase within one to two months follo\ving their 

 j)re})aration, especially on storage in the refrigerator. These ob- 

 ser\ations were rejieatedly and consistently made ^vith filtrates of 

 "agar washings" of meningococcus, B. d\se)ileyiac Shiga, B. coli, 

 and B. typhosus. It suffices to report the following examples: 



Meningococcus, Group I (44D) "agar washings" filtrates titrated May 5, 

 1930, showed 100 reacting units per 1 c.c, and May 27, 1930—700 reacting 

 luiits. A second batch of meningococcus. Group I titrated May 27, 1930— con- 

 tained 200 leacting units per 1 c.c, and June 10, 1930—1600 reacting units. 

 A third batch oi' filtrate of the same microorganism possessed 1000 reacting 

 units on May 15, 1930, and 2500 reacting units on June 30. 1930. 



Koplik in my laboratories made similar observations on fil- 

 trates of B. pertussis cnltnres in brain mediinn. 



FILTRATION AND DIALYSIS OF THE ACTIVE PRINCIPLE.S 



In my early experiments B. tyljltosus and meningococcus active 

 j)rinciples precipitated by satiiratic:)n with ammonium sulphate 

 did not diffuse through parchment membranes (Shwaitzman, 

 1929c) . Gratia and Linz (1932c) utilized a methcxl of dialysis 

 previously described by Gratia. 



A Petri dish was divided into t\\() sections by a very fine cello- 

 phane membrane. Sterile broth \\as poured into the two com- 

 partments separated by the membrane. The upper compartment 

 A\as inoculated ^vitli B. coli and the Petri dish A\as incubated for 

 three days at 37° c. There Avas an abundant gro^vth in the upper 

 compartment, whilst the broth in the lo^ver compartment re- 

 mained sterile. The fluids from bcjth compartments were cen- 

 trifuged and filtered. Rabbits ^vere prepared ^vith each of the 

 fluids and then injected intravenously with the respective fluids, 

 twenty-four hours later. The phenomenon could be produced 

 with the filtrate derived from the culture of the upper compart- 

 ment but failed with the filtrate of the lower compartment. 

 Similar experiments ^vere made ^vitli a collodion sac, filled ^vitll 

 sterile broth and placed in a tube containing sterile broth. The 

 broth of the sac was inoculated with B. coli and the apparatus 

 incubated at 37 "^ c. for four to fi\'e days. The broth in the tube 

 remained clear, whilst that in the inside of the sac became 



