ANIMAL PARASITES 83 



and hold firmly in position by a rubber band. The engorged insects 

 are then removed to another breeding cage and maintained on soaked 

 raisins for varying periods before dissection. The oocysts reach their 

 maximum size about the tenth day. 



Crows are very commonly infected by Hamiosporidia of the genus 

 Hsemoproteus (Halteridium), the forms in which McCallum first 

 worked out the significance of exflagellation. With living material 

 from this source the formation of the microgametes and the process 

 of fertilization can readily be demonstrated. 



Demonstration slides of Babesia bigemina and Babesia canis can be 

 purchased. 



For the practical work outlined it is, of course, desirable to use oil 

 immersion lenses. If this is not feasible it is quite possible to make 

 the study with the aid of high power dry lenses, supplemented by 

 demonstrations. 



CHARACTERISTICS OF THE HiEMOSPORIDIA 



The order Haemosporidia includes the blood-dwelling Sporozoa, 

 intracorpuscular or free in the plasma, and with or without 

 alternation of hosts. From the zoological viewpoint as well 

 as from that of human pathology the most important are the 

 malarial parasites belonging to the genus Plasmodium. Related 

 species of the same genus occur in sparrows and finches. Of 

 much importance in our Southern states is Babesia bigemina, 

 the organism of Texas fever of cattle. 



PRACTICAL WORK 



There will be furnished a slide of blood from a case of benign 

 tertian malaria, Plasmodium vivax. The preparation has been 

 stained in Wright's stain. Preparatory to the search for malarial 

 parasites in the slides furnished it is necessary to become 

 acquainted with the normal elements of the blood. Particularly 

 is it desirable to study the blood platelets and to distinguish the 

 types of leucocytes. For this purpose compare your findings 

 with the chart (Fig. 26). 



Plasmodium vivax. — Having completed this preliminary 

 examination, begin at one corner of the preparation and search 

 carefully the entire slide for various forms of the malarial parasite 

 in the erythrocytes, or red blood corpuscles. If the case from 

 which the slide was prepared was one of simple tertian malaria, 

 the parasites will be in approximately the same stage and slides 

 from other cases must supplement each other. Not infrequently 

 double or even triple infections may occur from bites of infective 



