60 THE ANIMAL PARASITES OF MAN 



plasma. The period of growth lasts six days, but the parasite 

 does not remain attached to the erythrocyte the whole time ; as 

 a rule it leaves the corpuscle at night, assumes the trypanosoma 

 form and moves about freely in the plasm until the next morning, 

 when again it attaches itself to a red blood corpuscle in order to 

 absorb nutriment. These alternating periods of movement and 

 rest follow one another until full growth is attained. Then a 

 multiplication stage sets in and the parasites multiply by con- 

 secutive longitudinal divisions until the products of division have 

 attained a minimum size. The small flagellates then attach 

 themselves once more to the erythrocytes, and the alternating 

 stages of growth and multiplication continue until the blood 

 literally swarms with parasites. 



By examining the blood of the owl one sees the asexual forms 

 of different sizes and in different stages of division, but one dis- 

 tinguishes also other forms with coarsely granular plasma and 

 fine pigment, which contain a small nucleus adjacent to the 

 blepharoplast, likewise quite small. These forms are the macro- 

 gametes, they penetrate the erythrocytes and grow more gradually, 

 accumulating more and more reserve material in their plasma. 

 They appear to change their host cells more rarely, and towards 

 the end of their growth are no longer able to assume the form 

 of trypanosomes. The mature macrogametes are quite unable to 

 leave their host cells, and are found surrounded by a pale residue 

 of the erythrocyte, the nucleus of which is then situated quite at 

 the periphery. 



The macrogametes are the only forms which persist at the end 

 of the acute stage of the halteridium disease, and after long 

 intervals they are capable of bringing about a relapse by repro- 

 ducing parthenogenetically the asexual forms. The macrogametes 

 arise from the asexual forms, and can be recognised even in their 

 earliest stages. The fertilisation of the macrogametes takes place 

 at the moment in which the parasites leave their intermediary 

 host. 



The microgametocytes also arise from the asexual forms, and 

 their nature may likewise be recognised in the earliest stages. 

 They are characterised by pale plasma, coarse pigment, large 

 nucleus, large blepharoplast. The mature microgametocytes give 

 rise to eight microgametes which develop as soon as the blood is 

 abstracted, but invariably perish within their mother cells when 

 left in the circulatory system of the bird. As soon as the macro- 

 gamete makes its exit from the avian host it becomes globular, 



