28 



all of these cultures, but great variation is shown in the amount of 

 pigment elaborated and in the formation of pellicle. The amount of 

 sugar present in the medium has an effect upon pigment production, 

 as noted in the descriptions of the separate cultures; the reaction 

 of the bouillon is also a feature, more pigment being produced ir. 

 bouillon of slightly acid reaction. Usually in sugar free neutral 

 bouillon B. prodigiosus I IV, VI, VII, and B. ruber miquel 

 show slight coloration of the liquid and a red surface ring, but 

 little true pellicle ; B. k i 1 i e n s i s and B. prodigiosus V give thick 

 orange red surface membranes, while B. plymouthensis,B. raini- 

 aceus, and B. prodigiosus VIII show color only in a pink or 

 violet surface ring, and B. ruber indicus usually lacks pigment 

 entirely in ordinary meat bouillon but produces it in abundance iu 

 a peptone solution. On the other hand B. rutilus and B. amylo- 

 ruber color the entire liquid deep red, in observing which fact 

 we may remember their recent isolation. 



Milk. All except B. amylo ruber and B. ruber miquel 

 acidify milk in 24 hours and coagulate it in from 24 (B. rutilus) 

 to 72 hours at room temperature. Some of the cultures show pep- 

 tonization of the casein. B. amyloruber does not coagulate, but 

 precipitates the casein, while B. ruber miquel produces no change 

 in milk except that of red pigmentation. Almost no variation is seen 

 in these reactions in milk. 



Gas production. The appended table shows that great vari- 

 ation is evinced in this respect, not only in the group, but in the 

 same organism at different times, with different stocks of bouillon. 

 The table gives only the limits of numerous determinations made 

 with neutral 1,5 /o dextrose bouillon. 



Table II. 



It is to be remarked that, except in the case of B. rutilus, 

 th relation of C0 2 to the total gas produced remains fairly con- 

 stant for each organism. B. rutilus produced 6065 %> C0 2 at 

 first, but with gradual loss, after isolation, of the power to produce 



