286 T^^ Philippine Journal of Science i9i7 



their shape depends considerably upon the stage of development. 

 If they are fully developed and have not reached the stage for 

 apparent reproduction, they are spherical and have a smooth 

 border. When they reach the stage for multiplication, either 

 equal or unequal fission takes place, thus breaking the evenness 

 of the contours and distorting the spherical shape. They may 

 assume slightly triangular, slightly oval, or various uneven, 

 spherelike shapes. Those recently divided are, as a rule, 

 spherical. 



Theiler, (7) in his extensive work on ahaplasma, states that 

 Anaplasma marginale is transmissible only in blood containing 

 corpuscles, as the organisms have lost their body plasma — for 

 which reason they derive their generic name— and have to exist 

 in the cell protoplasm, making them a strictly intercellular or- 

 ganism. He failed to produce the disease by injecting filtered 

 blood, proving that there was not a stage in the development 

 of the organism which was filterable. 



He also shows that the incubation period after the injections 

 of blood containing anaplasma depends upon two conditions. 

 If the amount of blood is large, the incubation period is short- 

 ened, and if the strain has been passed through several animals 

 by injection, the same result obtains. He finds this period to 

 average between sixteen and forty days, usually in the neighbor- 

 hood of from twenty-three to twenty-five days. 



He distinguishes two varieties of anaplasma, depending upon 

 their location in the red blood cells, the severity of the disease, 

 and the inability of one to confer complete immunity upon the 

 other. Anaplasma marginals is located upon or near the peri- 

 phery of the cell, and the other A. marginale (variety centrale) 

 is somewhat small and is located near to, or in, the center of 

 the corpuscle. It has not been noticed that A. centrale causes 

 death either by direct inoculation of blood or by tick infestation, 

 while animals affected with A. marginale frequently succumb. 

 An animal recovering from A. centrale infection, when inoculated 

 with the marginale variety, develops the disease, but in a much 

 milder form than would be otherwise encountered, which proves 

 that although there is not a complete immunity there is some 

 protection provided. 



The incubation period for this disease after tick infection is 

 rather long and has a wide range, varying from a few days 

 under two months to a few days over three months. 



Animals that were immune to Babesia bigemina could be 

 infected with anaplasmosis either by means of ticks or by 

 blood inoculation, which proved that B. bigemina afforded no 



