EQUINE MALARIA 347 
Etiology. Laveran who has studied this affection states that its 
cause is Piroplasma equi. It is closely related to P. bigeminum. It 
measures from 0.5 to 2.0u. During the invasion and multiplication 
of the parasites there is a high temperature. In the blood corpuscle 
the parasite is single, in pairs or in rosette form. The disease was 
believed not to be transmitted directly with the blood containing the 
parasite. Theiler, however, succeeded in proving that equine piro- 
plasmosis is inoculable with the blood of immune horses into suscepti- 
ble ones. The natural method of infection is not known, but it is 
believed to be by means of a tick. Berlitzer mentions Dermacentor 
reticulatus as the accepted carrier of the Russian tick fever of horses 
but he also suspects the biting flies. 
Theiler’s conclusions relative to the transmissibility of this parasite 
are as follows: 
The piroplasma found in the mule and the donkey is identical with 
Piroplasma equi first found in the horse. 
The disease caused by this piroplasma is inoculable with blood of 
immune animals into susceptible ones belonging to the domesticated 
species of the genus equus. 
The horse shows the greatest susceptibility for this piroplasma; the 
donkey is less, and the mule the least, susceptible. 
The possibility of ‘a practicable inoculation against the piroplas- 
mosis stands in the reverse order of the susceptibility. The mule 
may be safely inoculated with immune blood of any of the three 
respective equines; the immune horse-blood produces the severest 
reaction, the immune mule-blood causes little reaction, and so does 
the immune donkey-blood. 
The period of incubation is stated by Theiler to be 21 days. Mar- 
zinovski found the period of incubation from tick infection to be 12 
days. Nuttall places it at 16 to 17 days in the horse. 
Symptoms. An acute and chronic type are recognized. The 
acute type begins with a high temperature. There is jaundice, ap- 
pearing first in the eyes. Death follows rapidly, often at the time 
of the maximum temperature. In the chronic cases the symptoms 
are prolonged. 
The duration of the disease is from a few to several days. 
Morbid anatomy. The animal is emaciated. There is a rapid 
destruction of the red blood corpuscles. The blood is said to be thin 
and watery. The conjunctival subcutaneous tissue is of a yellowish 
