1 90 GENERAL BIOLOGY OF MICRO-ORGANISMS 



person who handles them. From the air, the milk may receive 

 further contamination (i) from flies coming to drink or perhaps 

 to drown without a clean bill of health from their port of last 

 departure, (2) from particles suspended as dust and containing 

 micro-organisms derived from manure, from hay and straw, 

 and from soil, and (3) moist droplets expelled from the mouth 

 and nose of the milkers and of the cattle. The subsequent 

 handling of the milk may add further kinds of bacteria from 

 human sources. Modern dairy practice in vogue in the produc- 

 tion of the higher grades of milk eliminates some of these sources 

 of contamination and minimizes the importance of the rest, but 

 nevertheless fresh milk of even the better grades contains a 

 great variety of micro-organisms, and often as many as 10,000 

 to 100,000 per cubic centimeter when it leaves the producer's 

 dairy. 



The usual milk flora derived from these various sources may 

 be classed under the following heads: 



A. Lactic acid bacteria. 



1. Bacterium (streptococcus?) acidi lactici 



2. Bacillus coli and B. lactis aerogenes. 



3. Long rods of B. bulgaricus type. 



4. Streptococcus pyo genes. 



5. Micrococcus acidi lactici. 



6. Acid formers which liquefy gelatin. 



B. Gelatin-liquefying bacilli. 



7. Rapidly liquefying types B. subtilis. 



8. Slowly liquefying types. 



C. Pigment-forming bacteria. 



D. Anaerobic bacteria B. welchii, putrefactive anaerobes. 



E. Special types causing peculiar fermentations, such as 

 slimy consistency, bitter taste and peculiar odors. 



F. Pathogenic organisms typhoid, tuberculosis, scarlatina, 

 diphtheria, diarrhea, septic sore throat, foot-and-mouth disease, 

 dysentery. 



G. Other fungi Molds, Oidia, Yeasts, Actinomyces. 



