THE PROTOZOA OR THE SIMPLEST ANIMALS 



149 



is conveyed through the bites of wood ticks is another 

 member of this group. x 



Many diseases of fishes are caused by other species of 

 sporozoans. The disease called "pebrine," which at- 

 tacks silk-worms and formerly caused very great losses 

 to the silk industry of France, is caused by a sporozoan. 



This is one of the comparatively few diseases which 

 can be transmitted from parent to offspring through the 

 egg. Louis Pasteur, a man famous for his valuable work 



FIG. 122. Skeletons of Radiolarians. (After Hseckel.) 



in establishing the germ theory of disease, discovered that 

 infected silk-worm moths could be distinguished from 

 the others by microscopic examination of the blood. This 

 fact made it possible, by rejecting the infected individuals, 

 to check the spread of the disease, which has since caused 

 much less damage. 



Although small in size the protozoa by their vast num- 

 bers are important factors in the life of the world. As we 

 have seen they produce many diseases in animals and man; 



