CRYPTOGAMS 311 



which are the active agents in the making of buttermilk 

 and cheese. 



The effects of their rapid multipHcation will be better 

 appreciated when we consider that bacteria are the smallest 

 of known living creatures. If lOOO of the influenza bacilli 

 were spread out in a single layer with their sides touching, 

 but not overlapping, they would not take up more room 

 than one of the periods used in punctuating this book; 

 and a coccus concerned in a tubercular disease prevalent 



445 446 



Figs. 445, 446. — Milk (highly magnified) : 445, pure, fresh milk, showing fat 

 globules ; 446, milk that has stood for hours in a warm room in a dirty dish, show- 

 ing fat globules and many forms of bacteria. 



among cattle in South America has recently been discovered, 

 of which double that number could be accommodated in the 

 same space. 



352. Distribution of bacteria. — Ordinary air, when free 

 from dust, contains, on the average, not more than five 

 germs to the liter — equal to about 1 for every 12 cubic 

 inches. Pathogenic, or disease-producing, germs seldom 

 occur in ordinary fresh air, and even when present are, under 

 ordinary circumstances, harmful only to people whose 

 bodies, by reason of physical weakness or unhygienic habits, 

 offer a congenial soil for their multiplication. Numerous in- 

 stances are known in which perfectly healthy persons have 

 carried about infectious disease germs in their bodies and 

 even transmitted them to others without experiencing 

 any inconvenience, or even being aware of their presence. 



