78 



PHYSIOLOGICAL ACTIVITIES OF THE PROTOZOA 



plant and animal tissues, dissolved in the water. Other saprophytes 

 live upon the juices in blood or other fluids of the animal body which 

 are similarly taken in by osmosis; these, however, belong to the group 

 of parasites or commensals, the difference between the two being 

 largely one of degree only, a parasite exerting some deleterious effect 

 upon the host, while a saprophyte and a commensal are harmless. In 

 all such cases the protozoa multiply in the region, such as a water 

 supply, or the fluids of the body, where food is most abundant and 



Fig. 25 



•«'«f'i!>'> 





v:. 



B C D E 



Digestion in a foraminiferon. (After Verwoin.) A-E, successive stages in the disintegration 

 of a ciliate (Colpoda) in a pseudopodium of Lieberkiihnia. 



where they are least disturbed by environmental factors. Thus, we 

 would account for the immeasurable swarms of chilomonas in a meat 

 infusion, or quantities of opalina in the frog's rectum, or the mwiads 

 of cytoryctes and neuroryctes in skin and brain of victims of smallpox 

 and rabies. 



In the higher animals solid food materials are taken into the food 

 receptacles of the body, where a secretion from the lining epithelial 

 cells is poured upon them, the food matter not coming in close contact 



