THE PATHOGENIC PROTOZOA 185 



different parasites in the malignant form, and they are 

 often classed together as ' the parasites of sestivo- autumnal 

 fever.' 



The main distinction between the benign and malign 

 species is that in the case of malign parasites flagella are 

 produced from crescent bodies, while in the case of the benign 

 parasites they are produced from simple spheres. Crescent 

 bodies are always found in malign fevers, though not in 

 the early stages. They continue in the blood for many 

 days or weeks, and are much less affected by quinine 

 than the other varieties. 



The Sexual Phase. Within the human host asexual 

 development alone takes place, but a sexual phase occurs 

 in the mosquito. Amoabulae become specialised into male 

 cells (microgametocytes) and female cells (mac regain eto- 

 cytes). The microgametocytes develop four to eight 

 filaments (gametes), which break away to fertilise the 

 large spherical and granular macrogametes, forming a 

 ' zygote,' spoken of at this stage as a ' travelling vermicule.' 

 This becomes encysted in the stomach wall. This grows, 

 divides into eight to twelve ' zygometres,' each of which 

 becomes a spherical ' blastophore ' and develops numerous 

 slightly sickle-shaped, radially disposed bodies, or zygoto- 

 blasts. When mature the blastophore disappears, the 

 capsule ruptures, the zygotoblasts are poured into the 

 body cavity of the insect, and make their wajr to all parts, 

 including the salivary glands, whence they are discharged 

 by the middle stylet of the proboscis when the insect 

 ' bites ' its next victim. The ' blasts ' then become 

 attached to corpuscles, and develop into the ordinary 

 form of malaria parasite. 



Flagellated bodies do not, apparently, occur in fresh 

 human blood, but are found when wet specimens have 

 been under the microscope for some time. The pigment 

 granules become arranged in the form of a central ring, 

 and afterwards show a peculiar vibratory movement, 

 which is apparently caused by the flagella which have 

 formed within the sphere. At this stage the flagella 

 shoot through the walls of the envelope of the sphere. 

 The flagella, which are usually from three to six in number, 

 are very delicate, actively moving filaments often having 

 a bulbous swelling at their ends. They frequently break 

 away and swim free in the blood. 



