226 



ZINDER AND LEDERBERG 



The production of FA in response 

 to chemical stimuli has not yet been 

 sufficiently controlled to give consis- 

 tent yields needed for experimental 

 use. However, when a filtrate contain- 

 ing little or no FA is prepared after 

 treatment of LA-2 with such agents as 

 crystal violet or penicillin and rein- 

 oculated into broth with LA-2, FA 

 is released in large amounts. This pro- 

 cedure has been carried through for 

 five cycles. The apparent regenera- 

 tion of FA was probably due to a lyso- 

 genic phage which had been released 

 in the first treatment. The lack of a 

 reliable indicator for this phage has 

 hindered the analysis of this reaction. 

 However, it has been a useful tool for 

 the evocation of FA from a single 

 strain without the introduction of 

 extraneous bacteria or viruses. 



Morphological a?id physical studies. 

 FA has been quantitatively sedimented 

 and recovered in the Spinco ultracen- 

 trifuge at 100,000 G for 30 min. Partial 

 sedimentation occurred in the Inter- 

 national centrifuge with multispeed 

 head at 20,000 G. In these prepara- 



tions FA is, therefore, of more than 

 macromolecular dimensions. Filtration 

 through a series of gradocol mem- 

 branes (obtained through the cour- 

 tesy of Dr. S. E. Luria) was also used 

 to estimate the particle size. Ten to 

 twenty per cent of FA were retained 

 by a membrane of A.P.D. 420 niju, sev- 

 enty per cent at 230 and 170 m^, and 

 ninety-nine per cent at 120 m,n. These 

 results indicate a particle size slightly 

 less than 0.1 ^ (Bawden, 1950). 



FA preparations exhibit numbers of 

 small, barely resolvable, granules un- 

 der the phase contrast microscope. 

 Electron micrographs show granules 

 whose size is in rough agreement with 

 the estimates of FA from filtration ex- 

 periments (figure 2). Some of the 

 granules agglutinated with anti-O 

 serum. Visible floccules which can be 

 removed by centrifugation appeared 

 in the reaction tube. However, the ac- 

 tivity remained intact in the super- 

 natant. Upon incubation with anti- 

 serum, some of the granules enlarge 

 and by four hours have attained sizes 

 of 5 to 8 ;i (see figure 11, Lederberg 



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Fig. 2. A partuli)- punhcd actnc liltratc, 4U,U(JU X. (Electron //ncrograph by Dr. 

 Paul Kaesberg.) 



