62 ZOOLOGY FOR MEDICAL STUDENTS CHAP. 



laid by Laveran (1880) who observed for the first time quite a number 

 of the stages in the life-history amoebula, merozoites, gametocytes. 

 He even observed the formation of microgametes though he interpreted 

 them as flagella and looked on their development by the " flagellated 

 body " as an abnormal process. Laveran definitely held that these 

 various appearances which he observed were stages in the life-history 

 of a parasitic organism and that that organism was the actual cause of 

 malarial disease,, but for a long period his views met with little acceptance. 

 In 1895 Ronald Ross fed mosquitos on the blood of a malarial patient 

 containing " crescents " and observed the formation of the " flagellated 

 body " within the insect's stomach. In 1897 a most important step was 

 made by MacCallum, who observing a parasite of the malarial type in 

 the blood of a " crow " saw the process of syngamy take place before 

 his eyes and consequently rendered clear the meaning of Laveran's 

 " flagellated body." Meanwhile Ross was continuing his investigations 

 in India. On feeding mosquitos (1897) with malarial blood containing 

 crescents he as a rule got no result, but in one kind of mosquito with 

 dappled wings he observed the parasites after 4 to 5 days lying embedded 

 in the wall of the stomach, in the form of round cells containing the 

 characteristic melanin pigment. Ross concluded that he had now 

 found the normal insect host of the parasite, and although he does not 

 name the mosquito it is clear from his description that it belonged to 

 the genus Anopheles. Circumstances interfering at this point with his 

 work on human malaria Ross carried on his experiments with a malarial 

 parasite (Proteosoma) of Birds and was able (i) to show that in this 

 case the transmitting insects were mosquitos of the genus Culex and 

 (2) to work out practically the whole sporogony cycle. The working 

 out of the corresponding details in the parasite of human malaria 

 within the body of the Anopheles is due in great part to Grassi and his 

 Italian colleagues (1898) and the final completion of the life-history 

 may be said to have been achieved by Schaudinn (1902) who was able 

 to observe the sporozoite actually attacking the blood-corpuscle. 



The group Sporozoa includes a great variety of Protozoa which are 

 linked together by certain common features. They always live as 

 parasites within the bodies of other animals. They are, in the full- 

 grown condition, without cilia or flagella. Their surface protoplasm is 

 condensed to form a thin pellicle without any openings and correlated 

 with this they feed by simply absorbing nourishment through the general 

 surface of the body. They fall naturally into two main groups according 

 as to whether the reproductive processes are distributed through the 



