42 PRACTICAL PARASITOLOGY 



a pathological significance in hatcheries and aquaria. Four flagella 

 spring from that end of the organism which is posterior when swim- 

 ming, and of these the two longer serve to attach the parasite to the 

 skin of its host, while the shorter pair are employed to obtain food. 

 These parasites excite an increased secretion of mucus on the part of 

 their host, which causes a characteristic dulness of the skin in fish 

 so affected. Owing to this increase in the mucous secretion, the 

 parasites may be damp-fixed in cover-glass preparations. 



Order 3. Binucleata. 

 (Hcemc flagellates and Hczmosporides.) 



These Protozoa are parasitic in the blood of vertebrates. Except 

 in the case of certain species (Trypanosomes), their flagellate nature 

 is not immediately apparent. In the greater number of species, the 

 adaptation of the organism to cell-parasitism has so completely 

 modified the flagellate apparatus, that it is customary to class them 

 together as a special order (Haemosporides) of the Sporozoa. Quite 

 recently, transition forms have been discovered which render it 

 impossible in the present state of our knowledge to draw a sharp line 

 between the Haemoflagellates and the Haemosporides. 1 Hartmann 

 includes both in the term " Binucleata " and treats them as an order of 

 Flagellates, distinguished by the peculiar structure of their flagellate 

 apparatus. In both there is a functional double nucleation ; in 

 addition to the principal nucleus, there is a special flagellar nucleus, 

 with which the flagella, generally one and more rarely two in number, 

 are connected. Although this basis of classification is not, as yet, 

 accepted by all authors, it is expedient for the present purpose to class 

 the blood parasites together, especially as the method of examination 

 is the same in all cases. 



(a) GENEKAL DIRECTIONS FOR OBTAINING AND EXAMINING 



MATERIAL. 



(1) METHODS OF OBTAINING MATERIAL. 



Those blood parasites which are pathogenic in man and animals 

 are restricted in their distribution almost exclusively to hot climates, 

 hence fresh material is to be obtained occasionally only and by importa- 

 tion. In Germany, two species of blood parasite have, up to the 

 present, been observed. These are, Plasmodium vivax, the parasite of 

 tertian fever in man, which I have myself observed in the flat country 



1 See M. Liihe, " Die im Blute schmarotzenden Protozoen und ihre nachsten 

 Verwandten," Menses Handb. d. Tropenkrarikli., vol. iii, Leipzig, 1906, pp. 69-268. 



