522 



TEXTBOOK OF BOTANY 



CIRCUMFERENCE OF 



BACILLUS PRODIGIOSIS 



DIAMETER 750 -mfi- 



INFLUENZA VIRUS 1 20 wn 



VIRUS OF TOBACCO MOSAIC 430X12.3 



TOBACCO RING SPOT VIRUS 180 x 10.4, 



STAPHYLOCOCCUS 

 BACTERIOPHAGE 90 irif,. 



O 



TOBACCO BUSHY STUNT 

 VIRUS 28mfi. 



o 



VIRUS OF YELLOW FEVER 

 22t„u. 



HAEMOGLOBIN MOLECULE FOOT AND MOUTH DISEASE 



2.8x0.6m|«. VIRUS 10 -mfi. 



EGG ALBUMEN MOLECULE 

 1.8X0.6 my. 



Fig. 230. Diagram illustrating the sizes of several viruses compared with those 

 of certain bacteria, bacteriophage, and protein molecules. On the same scale the 

 diameter of a human red blood corpuscle would be 3.5 feet. Data from W. M. 

 Stanley. 



individuals. This process may continue indefinitely. At suitable tempera- 

 tures divisions may occur as often as every 20 minutes, which is the 

 same as saying that an individual may exist but 20 minutes. A little com- 

 putation will show that within a day the number o£ such rapidly dividing 

 bacteria becomes enormous. If division occurred every 30 minutes, 

 starting with one bacterium, we would have: At the end of 24 hours, 

 281 million million bacteria = 1 pint in volume. At the end of 48 hours, 

 281 million million pints = about 32 cubic miles of bacteria. 



Such rapid increases of bacteria are limited to very short periods of 



