THE KINDS OF MICRO-ORGANISMS IN MILK 375 



non-motile type, named Granulobacillus saccharobutyricus im- 

 mobilis or Bacillus dimorphobutyricus. This latter occurs in 

 cow manure, and hence is common in milk. The spores of the 

 motile bacillus are not as highly resistant to heat as those of the 

 non-motile. The latter are destroyed only by prolonged boiling, 

 while those of the former are killed by three minutes' boiling. 



The Bacillus putrificus of Bienstock belongs to this group of 

 anaerobic bacteria, and is frequently found in milk. The spores 

 of this organism are also terminal, and are destroyed by five min- 

 utes' boiling, but not after three minutes. 



Weigmann's Plectridium fcetidum belongs to the spore-bear- 

 ing bacteria, and was isolated by the author from Limburger 

 cheese. It dissolves milk proteins with evolution of gas and a 

 strong odor of Limburger cheese. 



Butyric acid bacteria produce acid from milk-sugar, calcium 

 lactate, and protein. The chief products from carbohydrates are 

 lactic, acetic, and formic acids. Sometimes valeric acid and alcohol 

 also are formed. The gas consists of hydrogen and carbon dioxid, 

 hydrogen being produced in greater quantity than carbon dioxid. 

 From complex carbohydrates glycerin is sometimes produced. 

 The proteins yield chiefly butyric and succinic acids and are broken 

 down into albumoses, peptones, amino-acids, trimethylamin, am- 

 monia, ammonium carbonate, hydrogen sulphid, etc. 



Bacillus welchii and B. sporogenes are also common in milk, 

 as might be anticipated, and it is not at all improbable that these 

 organisms can be identified with some of the butyric acid bacilli 

 mentioned above. 



The propionic acid bacteria grow with difficulty, and at best 

 slowly on ordinary media. Weigmann recommends the follow- 

 ing medium for study of this type of bacteria: In 1000 c.c. of water 

 dissolve 20 grams of peptone, 2 grams of dipotassium phosphate, 

 5 grams of sodium chlorid, and 20 grams of calcium lactate. They 

 are anaerobes and decompose lactates, with production of carbon 

 dioxid, propionic acid, and some acetic acid. The casein is but 

 slightly broken up. They have been isolated from Limburger and 

 Emmenthaler cheese, and were formerly thought to produce the 

 holes or "eyes" in Emmenthaler cheese by evolution of carbon 

 dioxid. Other anaerobes sometimes occurring in milk which 

 produce capronic acid, butyl- and propyl alcohol have not been 

 sufficiently studied. Detailed descriptions of spore-bearing bac- 

 teria in milk are given in a study by Lawrence and Ford. 



As a rule, spore-bearing bacteria are not of material sanitary 

 significance in milk, and their chances for growth are relatively 

 poor, since milk is constantly in contact with air and contains 

 appreciable quantities of oxygen in solution. 



