30 MASS. EXPERIMENT STATION BULLETIN 319 



Behavior in Broth 



Arkwright (1921) and others have demonstrated that the rough colony variants 

 may form a pellicle and yield a sediment in the bottom of the tube, with the 

 supernatant fluid almost or entirely clear. Also, the growth of the rough type 

 is usually retarded. 



Table 5 shows the growth characteristics of the different variants in meat 

 extract broth (1 per cent Bacto peptone and .3 per cent Liebig's meat extract, 

 pH 7.0) at different incubation periods. The data show that 13 strains produced 

 normal growth in broth, while 14 variants exhibited modified growth characteris- 

 tics in this medium. It is interesting to note that strains D-l, D-2, IV-a, IV-b, 

 V-a, X-a, XH-a, and XV-a are characterized by a similar type of growth in 

 broth as well as on solid medium. Strains I-a and Il-a produced growth that was 

 slightly different in its nature from that of the aforementioned strains. The 

 sediment was more abundant and not so compact. It is of interest to note that 

 the variants which produced the so-called "roughest" colony produced growth 

 in nutrient broth that appeared quite typical or normal. These results show that 

 not all colony variant strains tend to settle out in meat extract broth. The 

 characteristic of settling in broth apparently cannot always be associated with 

 any definite type of colony or cellular form. Obviously, this property may vary 

 from time to time in a given type, since earlier in this investigation variants A and 

 B revealed a tendency to grow with difficulty and to settle out in broth. The 

 colonial and cellular features were not observed to have changed in these two 

 instances. 



Table 5. — Behavior of variants in broth. 



•Refer to Table 1 f'>r history of variants. 

 Legend: X — uniform heavy turbidity 



H slight clearing 



2-i partial clearing 



3-j marked clearing 



4H complete clearing 



(g) — granulai precipitate 

 (f) — Haky precipitate 

 (r) — ring formation 



