‘QUALITATIVE ANALYSIS OF MARKET MILK. ° 69 . 
from the milk ducts in many cases, are most abundant in fresh 
milk, but largely disappear in older milk as the lactic bacteria 
become abundant. ‘Their lack of action upon milk has led us to 
group them together without attempting further differentiation. 
Group V. Yellow coccus group. We have found almost uni- 
versally in milk of this region coccus forms that produce yellow 
colonies. They grow both: below and on the surface, and are 
sometimes a faint and sometimes a very brilliant yellow. There 
appears to be two types, one producing an acid colony, No. 231, 
though it fails to curdle milk, and the other developing a col- 
ony with no trace of acid. ‘These two types we have placed 
together in one column in our tables, although they are readily 
differentiated upon our plates. Some of the cultures prove to 
be a species of Sarcina (Sarcina lutea), while others are typical 
Micrococci, the cocci being almost always grouped in fours, in- 
dicating division in two planes only. ‘Their action upon milk 
is very slight. 
Group VI. Rapid liquefying group. These are character- 
ized by a gelatin colony liquefying with great rapidity, so that 
a single colony will liquefy a whole plate in two to three days. 
There are three or four species here included, but we have as 
yet made no attempt to differentiate them. One of the com- 
mon species is B. fluorescens liguefaciens, and another is B. 
subtilis, "They are distinctly putrefactive species, and their 
presence in milk in abundance will undoubtedly render it un- 
wholesome. ‘They are never very numerous in milk, and the 
few present in fresh milk are usually overcome by the lactic 
bacteria, so that they are not found in older samples of milk. 
This group of bacteria proves to be the most serious obstacle 
to a successful differential analysis of milk. The spreading of 
the liquefying area rapidly involves the whole plate, and if 
these colonies are numerous, the gelatin is all liquefied before 
it is in condition for study. Even three or,four such colonies 
may ruin a plate, and if the sample of milk contains members 
of this group, the analysis is sure to be difficult, uncertain, and 
sometimes impossible. Various attempts have been made to 
meet the difficulty. ‘he use of agar instead of gelatin is not 
satisfactory, since these bacteria are likely to spread over the 
whole surface and produce about as much trouble as in gelatin; 
