388 BIOLOGY OF THE PROTOZOA 



the best account of intestinal amebae is given by Dobell (1919). 

 For a clear comprehension of this modern point of view, I have found 

 it expedient and instructive in teaching to divide the history of 

 amebic dysentery into four arbitrary periods with the understand- 

 ing that no period is clearly marked but all grade into one another 

 in a slow, often backward, but nevertheless sure development. I 

 would designate these periods: (1) Early taxonomic observations; 

 (2) early etiological observations; (3) taxonomic chaos; and (4) 

 modern point of view. 



1. Early Taxonomic Observations. —With our present knowledge of 

 the intestinal protozoan fauna of man it is difficult to decide whether 

 so-called amebae of the earlier observers were really rhizopods or 

 more or less abnormal forms of intestinal flagellates. The so-called 

 "amebae" mentioned by Lambl (1860), who is usually credited 

 with the discovery of human intestinal amebae, are regarded by 

 Dobell as degenerating individuals of Trichomonas, while the value 

 of his observations is further lessened by the fact which has been 

 frequently pointed out, that he also observed the free-living forms, 

 Diffkigia and Arcella, in the same intestinal material. Ten years 

 later (1870) Lewis, in India, whose investigations had already 

 yielded a new mammalian trypanosome, and Cunningham (1871), 

 working on cholera, discovered an intestinal ameba they believed 

 to be non-pathogenic and which may well have been some harmless 

 species of Endameba, possibly coli. 



The first authentic association of an ameba and dysentery was 

 described by Losch (1875) in Russia. Upon autopsy of an indi- 

 vidual who had a well-developed hospital case of dysentery but 

 died of pneumonia, Losch found an abscess of the liver containing 

 amebae. Mainly negative results followed attempts to infect dogs 

 with material from fresh stools of the victim, and Losch concluded 

 that with only 1 dog showing dysentery symptoms while 3 were 

 negative his ameba, which he named A. coli, was a harmless com- 

 mensal living in the human intestine. There is little doubt in the 

 minds of modern students that he was really dealing with the active 

 agent of amebic dysentery, in which case, as Dobell, Wenyon, 

 Doflein-Reichenow and others have pointed out, the taxonomic 

 specific name of the dysentery ameba should be coli. Losch's 

 dictum, however, that his Amoeba coli was a harmless commensal 

 has influenced all subsequent investigators until the name coli is 

 so intimately associated with what has turned out to be a really 

 harmless ameba that it would involve needless confusion if an 

 attempt were made to apply rigorously the rules of scientific nomen- 

 clature. 



While the specific name coli thus got oft' to a poor start, the generic 

 name Ameba for endoparasitic forms was destined to have a short 

 life. Leidy (1879), who was working on his classical monograph'on 



