30 . THE ANIMAL PARASITES OF MAN 



the exterior, and in some species into the surrounding plasma. Movements 

 are effected by means of pseudopodia, processes of the protoplasm which 

 may be projected and retracted from any part of the body. Notwith- 

 standing the fact that this causes a continuous change of shape, the form, 

 number and arrangement of the finger-like or lobulate pseudopodia are 

 characteristic of each species, and together with the size, which fluctuates 

 between croi and 0-5 mm., and the structure, as well as the number of 

 nuclei and the constitution of the protoplasm, serve to distinguish the 

 species. The food, consisting of the tiniest organisms (bacteria, algae, 

 protozoa) or residues', is ingested by, the body, with the assistance of the 

 pseudopodia, i.e., is ingulfed by the protoplasm. 



Propagation takes place by means of segmentation, after previous direct 

 or mitotic division of the nucleus. After the completion of encystment 

 and after the successive segmentation of the nucleus into many parts, there 

 occurs a division into numerous segments, each containing a nucleus. The 

 division either involves the entire plasm or leaves a residual body. 

 After leaving the cell-membrane the segments assume an amoeboid or 

 flagellated form, and in this condition they are capable of propagation 

 through longitudinal division. Finally, they give up flagellate movement, 

 sink to the bottom, and continue to move by the means of pseudopodia. 



The amoebae live chiefly in stagnant fresh water, creeping about at the 

 bottom of puddles or on plants ; a few species are marine, others live in 

 moist soil, and a number are parasitic. In no case has there been satis- 

 factory evidence to prove whether the amoebae are facultative or true 

 parasites. 



All the amoeba-like beings one comes across in the open, or in infusions 

 or cultures, are not independent organisms, but developmental forms of 

 other animal, or particularly vegetable, organisms ; this, perhaps, is also the 

 case in some of the parasitic forms : the task of distinguishing the latter 

 from body cells is very often difficult. 1 



i. Amoeba coli, Loesch, 1875. 



Form, roundish or pear-shaped ; size fluctuates between 0*008 

 and 0-05 mm. The ectosarc can hardly be recognised in the 

 quiescent creature, but is distinctly visible in the pseudopodia ; 

 lhe endosarc is more or less finely granular, and usually contains 

 white and red blood corpuscles taken up for food ; it may also 

 contain eosinophile cells, bacteria, epithelial cells and particles of 

 faecal matter ; the pseudopodia are broad, lobose, one or two 

 being protruded at a time. The activity of the movement 

 depends on the temperature and on the constituents of the 

 surrounding medium : when the contents of the intestine have an 



1 The literature on this subject is found in Biitschli, I.e. in R. Behla, Die Amceben 

 vom paras, und culturell Standpunkt (Berlin, 1898, 8vo, with one plate) ; also in A. Lang, 

 Lehrb. der vergl. Anat. der wirbellosen Thieve, 2nd edit. (Jena, 1901, 8vo, with 259 

 illustrations) Compare also Feinberg, " Ueber Amosben u. ihre Unterscheidung von 

 Korperzellen (Fortschritte der Medic., 1899, xvii., p. 121). 



