BACTERIA IN FOODS 189 



qualitative one. The kinds commonly found may be class- 

 ified thus: 



1. Non-pathogenic; fermenting and various unclassified 

 micro-organisms. 



2. Pathogenic; tuberculosis, typhoid, cholera, scarlet 

 fever, diphtheria, and suppurative diseases have all been 

 spread by the agency of milk. 



i. The Fermentation Bacteria 



At the most we can make a merely provisional classifica- 

 tion of these processes. Many of them are intimately re- 

 lated. Of others, again, our knowledge is at present very 

 limited. It may be advisable, before proceeding, to con- 

 sider shortly what are the constituents of milk upon which 

 living ferments of various kinds exert their action. A 

 tabulation of the chief constituents would be as follows: 



f (i) Water 87.5 per cent. 



Ordinary (2) Milk-sugar 4.9 " " 



fresh milk = <j (3) Fat 3.6 " " 



100 per cent. (4) Proteids (casein, etc.). . 3.3 " " 



[ (5) Mineral matter 0.7 " " 



100.0 



Another mode of expressing average milk constitution 

 would be thus: 



Fat 4.1 per cent. 



Solids not fat.. 8.8 " " 



12.9 " 



It is probably too obvious to need remark that milks vary 

 in standard, but the above figures may be taken as authentic 

 averages. 



