320 BACTERIA 



Reaction is judged by three signs, namely, a rise of tem- 

 perature 2-3 C., a large " soup-plate " swelling at the site 

 of inoculation, and an enlargement of the lymphatic 

 glands. 



Swine fever, foot-and-mouth disease, chicken cholera, dysen- 

 tery, rinderpest, and other diseases of animals have micro- 

 organisms intimately related to them. 



There is a group of diseases due to the presence in the 

 blood or tissues of hcematozoa, that is, protozoa which can 

 live and perform their function in the blood. Amongst 

 these are malaria, sleeping sickness, and other tropical dis- 

 eases in man, and surra and various hsematozoa in horses, 

 fish, frogs, or rats, 



Malaria. Although a Bacillus malaria has been de- 

 scribed as the cause of this disease, it is now almost univer- 

 sally supposed that the true cause is a protozoan parasite. 

 In 1880 Laveran first described this organism, and the 

 discovery was confirmed by Marchiafava, Celli, and others. 

 Laveran claimed that it occurred in four different forms 

 during the progress of its life-history : 



(a) Spherical or Irregular Bodies attached to the blood 

 corpuscle, or free in the blood plasma. They are a little 

 smaller than the blood-cells, and may or may not contain 

 pigment. They eventually invade the corpuscles, possess 

 more pigment, and lose their amoeboid movement. Within 

 the red blood corpuscles they increase in size until they reach 

 the adult stage. 



(b) Segmentation Forms, often assuming a rosette shape, 

 follow next. They are pigmented, are possibly a sporing 

 stage, and are finally set free in the blood. 



(c) The Crescents, or Semilunar Bodies, are free in the 

 blood, but motionless. They are colourless, have a distinct 

 membrane, and generally show a little pigment about the 

 middle ; they taper towards the poles. They appear in the 

 blood after the fever has existed for some time, occurring 



