422 DISEASES OF THE BLOOD. 



of parasites and infected blood corpuscles is generally in direct ratio 

 to the intensity of the infection. These parasites are found through- 

 out the blood, but principally in that of the spleen, kidneys, and 

 mesenteric veins. They are only abundant whilst the temperature is 

 rising or at the moment when it reaches its highest point, and they 

 often disappear before death or convalescence. 



The pyriform shape is only temporary, and corresponds to the acute 

 phase of the disease, but the parasite assumes the round form as soon 

 as convalescence sets in. This round form gives birth to one, two or 

 three spherical spores, which are set free in the plasma after the 

 destruction of the maternal protoplasm, and are able after trans- 

 ference to a fresh red blood corpuscle to again assume the pyriform 

 shape peculiar to the grave forms of disease. 



The parasite can only be cultivated in defibrinated blood from a 

 haemoglobinuric subject, and the cultures do not always yield more 

 than reproductions of the round form, the pear-shaped form only 

 being produced with red blood corpuscles in the living animal body. 



Regarding the method of growth of the piroplasma in the body and 

 in cultures, Lignieres believes that the parasite may produce two forms 

 of spores differing in their nature. One, the active spore, has little 

 resisting power. It soon degenerates outside the animal body, forms 

 rapidly at the expense of one of the pear-shaped parasites, and may 

 immediately reinfect another red blood corpuscle. The other, called 

 the passive spore, is very resistant, and retains its vitality for a long 

 time outside the body, being produced at the expense of spherical 

 parasites already withdrawn and incapable of producing the disease. 



The form of piroplasmosis at present under consideration is peculiar 

 to the ox, and none of the other domestic animals or experimental 

 subjects can be inoculated with it. 



Subcutaneous or intravenous inoculation of the ox with 5 to 10 

 cubic centimetres always gives positive results when made with blood 

 or active products, such as the pear-shaped parasites or active spores, 

 but is ineffectual when the parasites have already begun to retract 

 in order to form passive spores. 



Calves i-eldom contract more than the benign form of the disease, 

 and do not die. 



In the grave form following experimental infection the temperature 

 begins to rise between the third and sixth day, and corresponds with 

 a marked increase in the number of parasites to be found within the 

 red blood corpuscles. The urine at first becomes albuminous, then 

 htemoglobinuric, whilst the red blood corpuscles diminish in number 

 to a very marked extent, falling from about six or seven millions to 

 one million, or even a tew hundred thousands, in the course of a few 



