414 AGRICULTURAL AND INDUSTRIAL BACTERIOLOGY 



found within a single blood corpuscle. The organisms are 

 from 0.5-2/i X 2 ~4M- The disease in cattle is characterized 

 by fever and by the presence of hemoglobin in the urine. 

 There is considerable destruction of the red blood cor- 

 puscles. In acute cases death often intervenes in from 5 

 to 8 days after the first symptoms. Most animals recover 

 but usually harbor in their bodies organisms for a long 

 period of time, though showing no symptoms of the disease. 

 The injection of blood from immune animals is widely 

 practiced as a method of vaccination in nonimmune cattle. 

 It results in a mild infection which immunizes against the 

 severe type when transmitted in the regular manner. 



The disease is normally transmitted only by the bite of 

 infected cattle ticks. The mature female tick gorges on the 

 blood of an animal, then falls to the ground and after a 

 time the eggs are laid. These hatch after from 19 days to 

 5 or 6 months, depending upon conditions, whereupon the 

 young ticks (called seed ticks) crawl up the stems of grass 

 and shrubs. They attempt to attach themselves to passing 

 animals. If they do not succeed, they die of starvation. 

 Ticks that have come from a mother that has fed herself on 

 blood from an infected animal are themselves capable of 

 transmitting the disease to the animal whose blood they in 

 turn suck. 



The disease is gradually being eradicated in the United 

 States. Within the last few years the line which marks 

 the northern border of the tick quarantine district has been 

 moved south until some of the southern states which for- 

 merly were in the quarantine district have been relieved 

 entirely. Within a few years the disease will probably have 

 been completely eradicated. 



THE GENUS PLASMODIUM 



The organisms belonging "to the genus Plasmodium are 

 responsible for the disease malaria in man. Three species, 



