50 ReEporT OF DEPARTMENT OF BACTERIOLOGY OF THE 
Peculiar pathogenic power characterizes many of the forms which 
were early designated as species. This characteristic was service- 
able both because it was easily recognizable and because it was the 
most important fact in connection with the organism. In the ab- 
sence of some single, definite characteristic, recourse has been had 
to reactions to various culture media. The difficulty here en- 
countered is that such reactions are often but an expression of the 
present physiological condition of the organism, this condition hav- 
ing been largely determined by the treatment to which the organism 
had been previously exposed. The examination of a large number of 
related species each of which is represented by a number of sub- 
cultures or strains will often furnish such a complete series of re- 
actions that no satisfactory division into species can be made. 
The initial flora of milk varies widely depending upon its en- 
vironment. When this milk is made into cheese the accompanying 
changes in temperature, moisture and acidity induce a rapid shift 
in this flora. The undeveloped condition of our classification and 
the difficulty of keeping living cultures of many of the forms until 
they can be directly compared with cultures isolated at a later 
date have, until recently, made it practically impossible to follow 
this change. 
When the study of germ life in any realm of nature is under- 
taken, attention is first concentrated upon finding media and con- 
ditions suitable for the growth of the germs present and the rela- 
tive success of various efforts in this direction is measured by the 
number of colonies which develop. Thus the first work is quanti- 
tative. When some measure of success has been attained in this 
line attention is next fixed upon so modifying the conditions as to 
make possible the division of the germs present into groups; that 
is, the work becomes qualitative. 
Up to 1904 our study of the bacteria in cheese was largely quanti- 
tative although we frequently isolated pure cultures and recorded 
their reaction upon various media. The improvements suggested 
by Conn & Esten? in the preparation of litmus gelatin, together 
with the beginnings of a classification which had then been made, 
encouraged us to undertake an intensive study both of the kinds 
of germs and the relative numbers in which they were present at 
various stages in the ripening of cheddar cheese. While the re- 


*Conn, H. W., and Esten, W. M. Qualitative analysis of bacteria in 
market. milki;..Conn. Agr:sExp:) Sta. (Storrs) sAmS Rptsers52863-01.. stood: 
see page 82. 
