Generic Characters in the Coccaceae 201 



and yellow chromogens, and included them both under the genus 

 Micrococcus. Fig. 3 makes it clear, however, that two distinct 

 centers of variation exist, one in the orange and one in the yellow, 

 and our correlation tables show that the two types of organisms arc 

 so radically different in every character as to demand their separa- 

 tion into distinct genera. Furthermore, it is evident that the orange 

 chromogens belong with the parasitic Paracoccaceae, and the yellow 

 forms with the Metacoccaceae. Nothing could show more clearly 

 how necessary it is to make a comparative study of a large series of 

 organisms in order to discern the true relationships of the bacteria. 



For this new genus we suggest the name Aurococcus, as indicat- 

 ing the orange color, which is its most obvious characteristic. Its 

 type-form is found on or in the plant or animal body. It occurs 

 in groups and short chains, stains by Gram, and produces a good, 

 but not heavy, surface growth of an orange color. It ferments 

 dextrose and lactose, producing an acidity generally between o . 5 

 and I. It grows well, but produces less pigment at 37°. It may 

 or may not reduce nitrates and liquefy gelatin. When it does liquefy 

 gelatin, it does so rather actively. 



Of the 158 cultures in this group, all show a good, but not very 

 abundant, growth of an orange color; 116 were obtained from the 

 body and 30 from the air, only 12 having a saprophytic origin; 147 

 show groups and short chains, but no packets; and 11 occasionally 

 give the sarcina grouping. Of the 158 cultures, 107 show a positive 

 Gram reaction, and only nine a consistently negative one. The aver- 

 age acidity in dextrose for the whole group is 0.7 per cent normal, 

 and for lactose 0.4 per cent normal. Of the 158 cultures only 

 six form less than o . 2 per cent acid, and 1 7 more than i per cent 

 acid, in dextrose. In lactose there is more variation; 53 cultures 

 give less than 0.2 per cent, and 11 more than i per cent, acid. 

 Of the cultures, 31 reduce nitrates, and 102 liquefy gelatin to an 

 average depth of 2.2 cm. — a very high value; while 56 organisms 

 fail to hquefy. The type-form of this genus is the commonest pyo- 

 genic organism, the M. aureus of Rosenbach. The non-liquefying 

 forms, those which reduce nitrates, and those which produce more 

 or less acid than is common in the genus, may later be set up as 

 separate species. 



