xm, b, 5 Haughwout: Flagellated and Ciliated Protozoa 219 



Days of the experiment. 



IS 23 21 



Fig. 1. Growth curves for dogs fed on fresh and autoclaved milk. Note the falling off 

 of growth between the twenty-seventh and the thirty-first day. Note also that dog 

 2, which was not infected with Ascaris, continued to grow at about the normal rate. 



The growth chart illustrating this case has been published 

 by Gibson and Concepcion(l8) and is reproduced here as fig. 1, 

 by kind permission of the authors. 



This is suggestive of the pernicious effects that may occur 

 as a result of heavy infections of protozoa of the so-called 

 "harmless commensal" type, particularly in very young children, 

 and is entirely apart from the menace they afford as possible 

 tissue invaders. It would seem that the end products of proto- 

 zoan metabolism, in cases where a host is heavily infected, could 

 not fail to affect the host unfavorably, particularly in the upper 

 intestine, where absorption is active. It is known that protozoa 

 in cultures may themselves succumb to the products of their 

 own metabolism, as has been shown by Woodruff (53) in a series 

 of experiments with the free-living infusorian Paramoecium. 

 In connection with the suggestion advanced by Gibson, it should 

 be borne in mind that the effects he noted may have simply 

 been those of starvation, through the appropriation by the para- 

 site of food designed for the host, an effect which would probably 

 be particularly noticeable in the case of a young and growing 

 animal. 



