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The dysentery bacillus. — Shiga, who discovered this organism, now 
recognizes 5 types, based on fermentative changes. This organism, 
like the typhoid bacillus, is “ hemiparasitic ” in the sense used by 
Herter; that is, it produces disease only when the bacilli have been 
introduced in considerable numbers or have had an opportunity to 
multiply owing to the feeble powers of resistance on the part of the 
infected individual. 
It seems that the nearer the various varieties of dysentery and 
typhoid bacilli approach the colon bacillus the less virulent they 
become. 
The dysentery bacillus has only been known since 1898 and its rela- 
tion to milk is not well worked out, but there can be little doubt that 
milk may by a means of spreading infection by this organism. 
The Bacillus proteus or proteus vulgaris . — This is a common organ- 
ism found frequently in normal feces in moderate numbers and com- 
monly contaminates milk. This bacillus produces the tryptic fer- 
ment that peptonizes casein and it also attacks carbohydrates. That 
this organism may induce acute diseases of the gastrointestinal tract 
appears to be well established. 
The tubercle bacillus . — Tubercle bacilli have frequently been found 
in milk, and their relation to disease is discussed elsewhere. 
Koch's cholera bacillus . — The specific cause of cholera requires an 
alkaline medium in which to grow. As milk is usually acid or soon 
becomes acid, the cholera vibrio has little chance of survival, though 
small outbreaks of cholera have been traced to milk. 
The Micrococcus melitensis . — This organism causes Malta fever 
and is found in goats' milk. It is fully discussed elsewhere in this 
bulletin. 
The Bacillus diphtheria . — The diphtheria bacillus finds favorable 
conditions for growth and multiplication in milk. A number of out- 
breaks of diphtheria have been traced to milk so contaminated. 
Streptococci and Staphylococci . — These form an exceedingly impor- 
tant group of organisms on account of their frequent and exceptional 
virulence. They are almost constantly found in milk, frequently in 
great numbers. Herter says that the human intestinal tract under 
normal conditions is probably most ol the time free from pathogenic 
varieties of this group of cocci. 
In healthy adults these pathogenic bacteria introduced with milk 
are ordinarily quickly destroyed in the upper portion of the tract. 
During infancy the digestive tract is very much less resistant to 
streptococcic infection. An invasion of the mucous membrane by 
streptococci is of frequent occurrence and may be associated with 
disturbances of almost any grade of severity. 
It has been shown by Bucher in this country, and by Escherich of 
Germany, that some of the severest forms of infantile ileo-colitis are 
