586 PIROPLASMA BOVIS 



become diminished and the urine in grave cases assumes a dark color. 

 The best method for making the inoculation experiments is to use 

 5 to 10 c.c. of defibrinated blood from an infected animal. 1 



Animals infected with such blood may acquire a fatal infection, or 

 the infection may take a moderately severe or even a mild course. 



Natural Mode of Transmission. Texas fever, in the natural course 

 of events, always is transmitted from an infected animal to a healthy 

 one by blood-sucking ticks. The tick which acts as the intermediate 

 host of the Piroplasma bigeminum in this country is called Boophilus 

 bovis, Rhipicephalus annulatus, or Margaropus annulatus. In 

 northern Europe piroplasmosis of cattle is spread by the tick, known 

 as Ixodes reductus. It is claimed that this tick also occurs in America, 

 and may here be concerned in the spreading of Texas fever. The 

 biting and sucking ticks probably discharge with their saliva an irri- 

 tating fluid which produces the local hyperemia and which also 

 introduces the protozoan parasites into the bitten animal. This 

 discharge of piroplasma from the intermediary host (the tick) to 

 cattle is similar to that of the Plasmodium malaria? by mosquitoes 

 (anopheles) into man. The developmental stages of the Plasmodium 

 malarise in the mosquito, however, are well known, while nothing is 

 known of such stages of piroplasma in cattle ticks. Mosquitoes do not 

 transmit the malarial parasites through their ova to their offspring, 

 but the eggs of a tick that has fed upon infected cattle will develop 

 ticks that spread the disease. 



A knowledge of the cattle tick, its life history and habits, is necessary 

 in the campaign to limit and exterminate the disease, and for this 

 reason the description given by Graybill in Farmer's Bulletin No. 

 378, United States Department of Agriculture, Washington Govern- 

 ment Printing Office, 1909, is here inserted : 



"In tracing the life history of the cattle tick it will be convenient 

 to begin with a large, plump, olive-green female tick, somewhat 

 more than half an inch in length, attached to the skin of the host. 

 During the few preceding days she has increased enormously in 

 size as a consequence of drawing a large supply of blood. 



"When fully engorged she drops to the ground, and at once, espe- 

 cially if the weather is warm, begins to search for a hiding place on 

 moist earth beneath leaves or any other litter which may serve as a 

 protection from the sun and numerous enemies. The female tick 

 may be devoured by birds or destroyed by ants, or may perish as the 

 result of unfavorable conditions, such as low temperature, absence 

 or excess of moisture, and many other conditions; so that many 

 which fall to the ground are destroyed before they lay eggs. 



"Egg-laying begins during the spring, summer, and fall months, 



1 Blood is defibrinated in the following manner: Allow blood drawn under aseptic precau- 

 tions to run into a sterile vessel containing some glass beads or fragments of glass. Shake well 

 for some time. The fibrin collects around and clings to the glass pearls, etc., and the defi- 

 brinated blood may then be poured ofr into another sterile vessel. 



