194 DOMESTIC ANIMALS, DAIRYING, ETC. 



be disease organisms, render it dangerous to use as a food. This 

 applies to both milk and milk products. 



A Brief Classification of Bacteria. From the standpoint of the 

 dairyman, bacteria may be briefly classified as follows: 1. Patho- 

 genic or disease producing bacteria, such as those of tuberculosis, ty- 

 phoid fever, scarlet fever and diphtheria. 2. Those that produce 

 poisons (ptomaines), not uncommon in ice-cream that has melted 

 and been re-frozen. 3. Peptogenic bacteria, or those that peptonise or 

 digest the casein or curd portion of milk. 4. Putrefactive forms of 

 germ life, which decompose the milk, producing offensive flavors and 

 odors. 5. Butyric ferments or those that act upon the fat of the 

 milk, producing rancidity. All are familiar with the taste and smell 

 of rancid milk, butter and cheese, due to this cause. 6. Bacteria 

 which bring about changes in the color of milk (chromogenic) pro- 

 ducing red, blue and other tints. 7. Sweet-curdling bacterial fer- 

 ments which cause the casein or curd portion of the milk to coagu- 

 late without souring. Their action may be compared to that of ren- 

 net. 8. Gas-producing organisms. Many of the organisms that pro- 

 duce bad flavors in milk and its products also produce gas. This 

 is particularly noticeable where milk is made into cheese, as the gas 

 is likely to produce holes or openings in it. 9. Lactic acid bacteria 

 which convert the sugar into lactic acid, or cause the ordinary sour- 

 ing of milk. 



This is not an exhaustive list, but will prove sufficient to illus- 

 trate the many and varied changes in milk and its products, due to 

 the action of germ life ferments. In fact the problem of ferments 

 and fermentations, and how to control them, is the great task which 

 the dairyman has to face in the handling of milk, the manufacturing 

 of it into its different products, and the care of the same. Some of 

 these organisms are decidedly harmful, and when present in milk 

 make it dangerous to use. Others affect its flavor, rendering it more 

 or less unpleasant to the taste and smell. The great majority, while 

 not specially harmful to a person in vigorous health, depreciate the 

 value of milk as a food and also, when present in too great numbers, 

 set up trouble in the digestive tracts of persons with weak digestion, 

 such as invalids and infants. Others, particularly the lactic acid 

 organisms, are what may be classed as desirable organisms, that is, 

 when not present in too great numbers, and when kept under control, 

 they aid cheese and butter makers in the process of ripening milk 

 and cream for their respective purposes. They are not desirable in 

 milk or cream' 1 to be consumed as such, that is, if allowed to develop 

 to any extent they cause it to sour. (Manitoba Agrl. Col. B. 3.) 



Bacteria. Science has admirably succeeded in tracing back 

 through generations the species, genera, families and orders of plants 

 and animals, but whatever may be the prototype of any living organ- 

 ism, the origin of that prototype, that first form of living substance, 

 is to-day as obscure as it was a thousand years ago. The same holds 

 true in case of bacteria. We simply have to admit that we do not 

 know. But this lack of information is of little consequence to the 

 practical dairyman. To him the knowledge of the general distribu- 



