ISABEL MULFORD. 229 
‘The culture media employed were boiled or baked 
potatoes, the whites of hard-boiled eggs, chicken bouil- 
lon, infusions of vegetables, milk, ete. The work with 
potatoes was most satisfactory. These were cut in 
halves or slices. Their cut surfaces were then touched 
to a dusty surface or left fora time exposed to the air 
in order to inoculate them with possible germs. The 
potatoes were then placed upon plates of glass, under 
inverted tumblers. Several interesting forms quickly 
appeared, and at varying intervals of incubation, these 
were followed by others. -The first cultures were of 
course badly mixed. It was not unusual to find several 
forms of bacteria contending for possession of the 
same slice, but by careful transfers, the species were 
separated, and a study of the development of individual 
- forms was rendered possible. I soon became embar- 
rassed with the richness of the field, so that I finally re- 
stricted my attention almost entirely to the chromo- 
genic or colored forms. These I considered as distinct 
Species, so long as their microscopic and macroscopic 
characters were constantly reproduced through succes- 
sive cultivations. According to Cohn, the pigmentary 
bacteria are veritable species ; for, first—their pigments 
offer the greatest diversity in chemical action and by 
Spectroscopic analysis ; second—each species, cultivated 
in the most diverse media, produces always the same 
coloring matter. 
It seems to be evident, that there are a number of 
Species indigenous to this country, as many forms can- 
not be identified with any described by the best German 
and English authorities ; still, it is quite possible that 
further investigation will develop relationships which 
are not now apparent, and at present the tendency is 
to reduce the number of species as much as possible. I 
ought to say that I took special precautions to insure 
cleanliness and freedom from outside germs in my cul- 
118 
