90 IOWA ACADEMY OF SCIENCES. 



into another channel, and lactic acid and, perhaps, other substances are produced 

 in place of the usual pigment." 



Investigation has shown that the flora of milk is a variable one, owing to cir- 

 cumstances under which they make their entrance. 



The normal milk from a healthy cow contains no germs. This is easily deter- 

 mined by using a sterilized catheter. The pails and water used to clean milking' 

 vessels and cans, the stable, hair from cows, and hands of milker, all have germs 

 that find their way into the milk. The species found are not only abundant, as 

 shown by various bacteriological studies of milk, but both good and bad occur. 



Cnopf and Escherich,"' found from 60,000 to 100,000 per c. c, in milk a few 

 hours after milking. Mr. B. F. White, in the writer's laboratory, found that 

 when milk was obtained in the ordinary way, and cultures made soon thereafter, 

 it contained 40,000 germs per c. c. Milk coming to the creamery had, in some 

 cases, as high as 1,976,000 per c. c. Prof. Conn^^* inierestingly shows the enormous 

 number in milk, as well as the great increase. The writer^'' has also brought 

 together the results obtained by Miquel, Weigmann, and others, on the enormous 

 increase, when milk is kept under favorable conditions for their development. 

 That our milk supply of cities contains an enormous number has been shown by 

 Sedgwick and Batchelder."" It is not to be wondered at that milk will sour in the 

 course of a few hours on a hot day in summer. 



The fact that different samples of milk left standing in a warm room will 

 develop quite different odors is due to particular germs. The practical dairyman is 

 well aware that he cannot always make butter of uniform quality, and this is owing 

 to injurious species. Experiments made during the last few years have shown that 

 by Pasteurizing milk and using the germs that have the right odor, butter of uni- 

 form and high quality may be produced. These results were first brought to 

 notice by Storch, of Copenhagen. Weigmann, of Kiel, has also experimented 

 with these germs in a practical way, sending them out to creameries. Prof. Conn, 

 of Middletown, Conn., writes me that he has had success in using one of his own 

 germs. 



Islo one questions the fact that odors and products of bacteria are very charac- 

 istic. Storch has called attention to butter that had a flavor of beets, but the ani- 

 mal from which the milk came had never been fed on beets. Dr. Jansen"^ 

 refers to a bacillus which was found in milk that produced a very 

 fetid odor, his Bacillus fceticliis. 



The writer has isolated a Bacillus which he has called Bacillus aiomaiicus,^*- 

 because of the powerful volatile odor produced. In some media it has an odor 

 characteristic of walnuts. Again it resembles limburger cheese, and a more inter- 

 esting fact is that it tastes like cheese. 



The importance of bacteria in ripening cream is very important, since cheese will 

 not ripen unless Bacteria are present. Duclaux,^''^ Adametz,"* Freudenreich,"^ and 



137 Abst. Centralb. Agrl. Chm., 1890, p. 575. 



138 The Fermentations of Milk, Office of E.xperiment Stations. Bull. No. 9, U. S. Dept. 

 of Agrl pp. 75, see p. 30. 



139 The Bacteria of Mlll<, Cream and Cheese. Report Fifteenth Annual Convention 

 of the Iowa Dairy Association, held at Waverly, 1891, p. 81. 



110 A Bacteriological Examination of the Boston Milk Supply. Boston Med. and 

 Surgical Journal. 18!j2, p. 25. 



liiCentralblatt Bakt u Parasitenkunde, Vol. XI p. 409. 



ii2Bull. No. 21, Iowa Agrl. Experiment Station, pp. 792-796. 



ii3Le Lait etudes chimiques et microbiologiques, Paris, 1887. 



i«Bakteriologische Unteruschungen ueber den Reifungsprocess der Ktese Landw 

 Jahrbucher, Vol. XVIII. p. 228. 



w5Landw, Jahrbuch der Schweiz, Vol. V, p. 16, Vol. IV, p. 17. 



