THE MILK CONTRACTOR 273 



aerobes. The latter group of organisms seemed to him particularly sig- 

 nificant, for the changes produced took place slowly and even though the 

 milk teemed with microbes, its abnormal condition might be overlooked. 

 The growth of the spore bearers would ordinarily be restrained by the 

 lactic acid bacteria ; so only in milk heated enough to destroy these lactic 

 organisms, would the spore bearers develop sufficiently to either change 

 the character of the milk or to endanger the health of children who might 

 drink it. Fliigge believed that the spores of the peptonizing bacteria 

 would resist the action of the gastric juice and finding proper conditions 

 for development in the lower bowel would multiply there and give rise 

 to the grave symptoms of intoxication seen in summer complaint. The 

 several organisms isolated from heated milk by Fliigge were later studied 

 by Gotschlich and Kaensche who found the principal anaerobe to be the 

 B. butyricus of Hueppe and the principal aerobes, B. subtilis, B. mesen- 

 tericus vulgatus and B. mesentericus fusus. 



Ford and Pryor examined milk of 21 dairies in Baltimore which repre- 

 sented nearly every sort of milk sold in the city and Ford continuing the 

 studies examined 24 specimens of raw milk from 17 different dairies and 

 27 specimens from eight sources of the commercially pasteurized milk of 

 Washington. The results in the two cities were essentially the same. 

 The investigators heated the milk to different temperatures, viz., 140, 

 149, 176, 185, 212F. and under 20 Ib. pressure for from 5 to 35 min. 

 according to the experiment, and incubated the heated or pasteurized 

 milk both aerobically and anaerobically at 71.6 and 98.6F. for 48 to 96 

 hr. The condition of the incubated sample was recorded and agar plates 

 poured from it. The presence of B. welchii was tested for by injecting 

 the incubated sample into the ear vein of a rabbit. The conclusions 

 arrived at were: 



1. As first pointed out by Fliigge, milk always contains heat resistant 

 spores of aerobic and anaerobic bacteria which by their development can 

 give rise to disagreeable and unwholesome changes in milk, converting 

 it from a food of great nutritive value into an undesirable, if not a danger- 

 ous, article of diet. 



2. These changes take place in milk heated to any temperature from 

 149 to 212F. and kept at any temperature from 71.6 to 98.6F., but 

 not at that of the ice box at 39.2 to 42.8F. 



3. Spores of these bacteria survive for a long time in milk kept on 

 ice and when such milk is transferred to higher temperatures they can 

 initiate their characteristic changes in it. 



4. The problem of pasteurization must be worked out on the basis 

 of changes that occur in milk heated 140 to 149F. 



5. The most important anaerobic species is B. welchii which is 

 believed to be universally present. Aerobic spore-bearing bacteria are 

 also found in practically all samples and belong in general to the group 



IS 



