NOVEMBEE 27, 1896.] 



SCIENCE. 



773 



response to the needs of the organism. 

 Even if PlanMomya should eventually prove 

 to be an immature Leptonoid, the fact of 

 the mode of development of the ctenidium 

 would remain of the greatest interest. The 

 existence of this minute form, apparently- 

 confined to the open sea between the lati- 

 tudes of Ascension Island and Bermuda, 

 suggests that the earliest (Cambrian) bi- 

 valves may also have been pelagic, which 

 would explain their rarity and minuteness. 

 Of the various larval bivalves found in the 

 Plankton, all are dimyarian and destitute 

 of a pallia! sinus, the oral palpi develop in 

 advance of the gills, which appear either as 

 a single lamella on each side or as a num- 

 ber of buds not exceeding ten, while the 

 hinge is either edentulous or taxodont; in 

 all these characters recalling the Paleo- 

 concha. "Wm. H. Dall. 



Smithsonian Institution. 



A STUDY OF THE COLON BACILLUS GROUP, 



AND ESPECIALLY OF ITS VARIABILITY 



IN FERMENTING POWER UNDER 



DIFFERENT CONDITIONS. 



A EESEARCH On the colon bacillus group of 

 bacteria has been in progress during the 

 past two years in the Laboratory of Hy- 

 giene of the University of Pennsylvania, in 

 accordance with a scheme prepared by Dr. 

 Weir Mitchell and Dr. John S. Billings, the 

 director of the laboratory, for an investiga- 

 tion on the variability of bacteria, under the 

 auspices of the Bache fund. A resume of 

 the results of last year's work was pub- 

 lished in this Journal under the title ' The 

 Influence of Certain Agents in Destroying 

 the Vitality of the Typhoid and the Colon 

 Bacillus,' and the following article records 

 the experiments made since that time. The 

 organisms which, owing to certain common 

 characteristics, are usually included in the 

 group under examination, the colon bacil- 

 lus group, have excited much interest dur- 

 ing the past few years because of their re- 



semblance to the bacillus of typhoid fever 

 and the difficulty attending the diff'erentia- 

 tion of certam varieties of the colon bacil- 

 lus from this organism ; and also because 

 of the importance ascribed in recent years 

 to the bacillus coli communis, the type of 

 this group, as a cause of inflammation and 

 abscess in man. This organism first isolated 

 by Escherich, in 1886, has been found to be 

 constantly present in the intestinal canal of 

 man, and als 3 in that of many of the lower 

 animals. Different observers have noticed 

 variations in the characteristics of cul- 

 tures obtained from diff'erent sources, and 

 some have been disposed to consider each 

 of these varieties to be a separate spe- 

 cies, but the similarity of many prominent 

 features of these cultures finally led to 

 a grouping of these organisms as varieties 

 of a species. Different groups of colon 

 bacilli have been described by several 

 writers. Achard^ and Renault in 1892 had 

 observed five types of the colon bacillus, 

 and Taver had isolated fifteen varieties. 

 Stoeklin^ distinguishes thirteen forms which 

 he classifies by their motility and the num- 

 ber of flagella. Gilbert* finds five varieties. 

 Fremlin^ describes several varieties obtained 

 from different animals. Refik® records five 

 varieties found in water. But an article 

 published by Dr. Th. Smith^, entitled 

 ' Notes on the Bacillus Coli Communis and 

 its Belated Forms,' in which several vari- 

 eties of the colon bacillus and other similar 

 organisms are tabulated, showing their dif- 

 ferentiation by means of the fermentation 

 test and also by the comparison of other 

 distinguishing reactions, has been the 

 means of making better known a number 

 of the different varieties and of establishing 

 a basis for further classification. Very 

 little comparison can be made, however, 

 between the varieties described hj Smith 

 and those by other writers because of the 

 paucity of the tests recorded by the latter. 

 Cultures from the species designated by 



