495 
especially numerous in milk that clearly contained pus or was known 
to be derived from cows vdth mastitis. At that time all streptococci 
were believed to be pathogenic, and it was assumed that when such 
organisms were found in milk they pointed to disease of the udder 
and were capable of propagating disease when ingested with the milk. 
Kecent investigators have so clearly demonstrated the close relation- 
ship existing between the micro-organisms, which cause spontaneous 
souring of milk, and the streptococci that it will be of interest to 
consider the former at some length. 
Pasteur, ® Lister, ^ Hueppe, and many others studied the souring 
of milk. Pasteur proved that micro-organisms were the cause, and 
Lister, twenty years later, isolated in pure culture a bacterium which 
he deemed the common agent. Subsequent bacteriologists have 
studied and described at length a great variety of bacteria found in 
ordinary dairy milk, capable of causing fermentation, with lactic acid 
formation. Many of these micro-organisms were later shown to 
have been introduced by unclean containing vessels and careless 
handling of the milk, and while capable of causing souring must be 
regarded as accidental and inconstant in occurrence. When drawn 
directly in sterile vessels with ordinary caution as regards cleanli- 
ness the variety of organisms is reduced to three or four. The 
technique of the early bacteriologist was somewhat imperfect, and 
cultural methods less exact than now. It is not surprising that 
identical bacteria were described by different observers as shovdng 
slight variations. 
A review of the work done since Hueppe in 1884 (who was the 
first to apply modern methods to the study of milk bacteria) shows 
that the common lactic bacteria may be classified in three groups. 
The first includes the bacilli of the type first described by Esche- 
rich,^ the Bacterium xrogenes group. These organisms are classified 
with the colon group and owe their presence in milk to contamina- 
tion with the feces of the cow. 
Marpmann,^ Grotenfeld,^ Loffier,^ Weigemann,* Kayser Clauss^ 
and others have described organisms of this type. They grow read- 
ily on ordinary media with all the characteristics of the colon group, 
a Ann. d. Chim. et Pliys., 3 Serie, 1858, 52. 
6 Quarterly Journal of Micros. Sc., 1878, 18, p. 177. 
cMitth. a. d. kaiserl. Gesundheitsamt, 1884, 2, 309. 
‘^Mitth. a. d. kaiserl. Gesundh. amt., Bd. 2, S. 309. 
« Darmbakterien des Sauglings, Stuttgart, 1886. 
/Erganzungshft. Centrbl. f. Allg. Gesundheitspfl., Bd. 11, S. 117. 
i/Fortschr. d. Mediz., Bd. IV, 1889. 
^Berl. klin. Wodienschr., 1887, S. 631. 
^Landw. Wochenbl. f. Schlesw. Holst., 1890, 29. 
J Annal. de I’lnstitut Pasteur, 1894, p. 738. 
^Inaug. Dissert., Wurzburg, 1889. 
