MORPHOLOGY AND BIOLOGY. 13 



Collections of stagnant water in almost every region 

 abound in amoebae, and in the tropics almost every 

 source of water supply is contaminated with these 

 organisms. They have also been found upon green 

 vegetables, especially salad vegetables, and it is not 

 at all improbable that they occur on all garden 

 produce in regions where human excrement is used 

 for fertilizing purposes. Fortunately only a small 

 number of species are pathogenic for man, as other- 

 wise almost every inhabitant of warm regions would 

 suffer from amoebic dysentery. 



GENERAL MORPHOLOGY. 



Roughly stated these organisms may be said to 

 consist of a mass of protoplasm containing a nucleus 

 and one or more vacuoles, which may or may not 

 be contractile in character. Reproduction occurs by 

 simple division, schizogony, gemmation, and repro- 

 duction within a cyst. They vary in size in different 

 stages of development, measuring from 5 /* to 70 t*> 

 or more in diameter, and are spherical or oval in 

 shape when not in motion. The size of the organism 

 alone cannot be used as a method of species differen- 

 tiation as it varies greatly at different periods of 

 growth. All amoebse present for description a cyto- 

 plasm and a nucleus, together with certain other 



