182 



PHYSIOLOGY OF MICROORGANISMS 



ated. The ultramicroscope makes it feasible to use Tyndall's phe- 

 nomenon effectively in revealing particles of some colloidal substances 

 and solutions having particles of larger dimensions. Siedentopf and 



Anthrax 

 bacillus 



aboum 

 6fj long 



Particles or colloid gold 



D Precipitated parhcle 

 oF gold, about- 75 ^Jfj 



Starch Chloroform Hydrogen 

 molecule molecule molecule 

 about0.8uu abou 



tn/argemenf- 1 000 000 to 1 



Particles of a fine mastic suspension 



Enlargement- 3333 to 1 



FIG. 108. Comparison of particles of different sizes. (Ostwald.} 



The large circle corresponds to the diameter of a human red blood corpuscle 

 (about 7.5 M); the large pentagon to that of a starch granule of medium size (about 

 7.0 n). The particles enclosed in a frame are, in comparison with the rest of the 

 figure, enlarged 333 times. 



The figure has been constructed from data and tables given in R. Zsigmondy 

 (Zur Erkenntnis der Kolioide, Jena, 1905). The values for the mastic suspension 

 are taken from /. Perrin's studies [Kolloidchem. Beihefte I, 221 (1910)]. 



Zsigmondy find that the microscope has its limitation of visibility at 

 about o.ifj. and the ultramicroscope at about i.ojuju (submicron) or 

 o.ooiyu. There are particles existing beyond the reach of the ultra- 



