DIFFERENTIA TION AND REJUVENA TION 139 



organism with scarcely any differentiation of its struc- 

 ture. The next of the slides shows us again another 

 of these parasitic simple organisms, namely Plasmo- 

 dium vivax, the cause of tertian malarial fever. The 

 tiny creature inhabits the blood corpuscles of man ; 



FIG. 4Q. TERTIAN MALARIAL PARASITE. Two 

 human blood corpuscles alongside and drawn 

 on the same scale, by E. S. Kilgore. 



when it enters the corpuscle it is very minute, 

 scarce an eighth of the diameter of the corpuscle ; it 

 grows very rapidly, feeding on and destroying the 

 corpuscle and yet meanwhile by its own growth caus- 

 ing the corpuscle to enlarge. Our picture, Fig. 49, 

 shows three human red blood corpuscles, two in their 

 normal condition, the third (on the right) distended 

 by the overgrown parasite, which is heavily charged 

 with pigmented granules, and almost completely fills 

 the corpuscle. The nucleus at this stage of the 



