MICHIGAN ACADEMY OF SCIENCE. 
73 
Acid will act as a catalyzer. An organism which produces a trypsin- 
like enzyme and at the same time forms acid in milk may be classified 
as a non-liquefier ; but if a milk culture of such an organism be made 
neutral or slightly alkaline marked proteolytic changes occur. Again, 
an organism which produces a pepsin-like enzyme and during its growth 
in milk forms alkaline compounds may be unable to cause proteolytic 
changes. This organism in association with a lactic becomes a liquefier. 
Within the cell of organisms are entracellular enzymes which are not 
diffusable. Entracellular proteolytic enzymes of dead cells in old cul- 
tures are liberated through autolysis. And their behavior is similar to 
that of an extracellular enzyme of like nature. 
Changes occurring in milk as a result of the associative growth of a 
lactic with another organism are influenced by the change in reaction, 
the accumulation of metabolic products of both the organism and the 
lactic, the temperature of growth, the accessible supply of oxygen, etc. 
However, the hindrance or encouragement in the production of enzymes 
offered by the lactic through its metabolic products to other organisms 
growing in association is a factor that cannot be overlooked. 
Michigan Agricultural College, 
East Lansing, Michigan. 
