Serum Fastness 



349 



definite a pellicle as the tubercle bacillus, or other pellicle form- 

 ing organisms. 



The acetone-ether soluble substances of staphylococci grown 

 in this way increased from 7.9 per cent, to 39.9 per cent. 



It was concluded that pellicle formation was due to the in- 

 creased amounts of acetone-ether soluble substances by virtue 

 of which the bacteria resist wetting, and are thus supported on 

 the surface of the medium by surface tension. 



The present study concerns the effect of wetting on the agglu- 

 tination reaction. 



A laboratory strain of the staphylococcus aureus was grown 

 in parallel cultures on ordinary broth and three per cent, 

 glycerin broth respectively. Rabbits were immunized with 

 killed cultures of the staphylococcus grown on ordinary broth. 

 In the interest of brevity the strain grown in ordinary broth 

 will be referred to as the "lean" strain and that grown in glycerine 

 broth as the "fat" strain. An agglutinating serum was thus ob- 

 tained which agglutinated the lean strain in a dilution of 1-90. 



Parallel agglutination tests were then made with the fat and 

 lean strains in serum dilution of 1-50. After four hours in the 

 incubator the lean strain was completely precipitated, while there 

 was no visible change in the tests with the fat strain. However, 

 after 30 hours there appeared to be some precipitation. At this 

 point a count was made to determine the percentage of bacteria 

 still remaining in suspension as compared with the control, — 

 which contained the same number of bacteria without the serum. 

 The count was made by a laboratory worker not personally in- 

 terested in the experiment. The count revealed that 30 per cent, 

 of the organisms had been precipitated by the serum, while 70 

 per cent, still remained in suspension. The test tube containing 

 the fat strain which had been in contact with the agglutinating 

 serum for 30 hours was then centrifuged and the supernatant 

 fluid removed, and to this supernatant fluid was added the proper 

 amount of the lean strain. Agglutination was found to be 

 prompt. This experiment indicates that there had been very 

 little adsorption of the antibodies by the fat strain. 



The fat strain was then cultivated on ordinary broth, making 

 daily transplants, and the agglutinability of each generation 

 tested. It was found that the agglutinabiliy of the fat strain 

 was completely restored after three generations of culture on or- 



