1038 PARASITES OF PROTOZOA 



of parasites, may be sufficient, however, to account for the effect of 

 Holospora obtusa. 



Calkins (1904) recorded an infection of the macronuclei of 80 per- 

 cent of Paramecium caudatiim, in preparations from one culture, with a 

 parasite that he named Caryoryctes cytoryctoides. The organisms appeared 

 as scattered bodies in parts of each nucleus, and have no resemblance to 

 Holospora or Nucleophaga. 



Bacteria are especially prevalent in the cytoplasm of many ciliates that 

 live in decaying matter, and Kahl (1930) stated that often these may 

 be regarded as symbionts (mutualists), rather than parasites. He showed, 

 for example, in Epalxis antiquorum, large symbiotic bacilli which Penard 

 (1922) had described as rods. Recently the occurrence and significance 

 of bacteria in sapropelic ciliates has been the subject of studies by Lieb- 

 mann (1936a, 1936b, 1937). 



Liebmann (1936a) found in Colpidium colpoda chlorobacteria that 

 appeared to live as facultative symbionts. They were enclosed in vacuoles 

 occurring more or less abundantly in the cytoplasm under conditions 

 of anaerobiosis and H^S content of the water, but not in the presence of 

 oxygen. Their appearance was definitely correlated with the amount of 

 H2S. Similar chlorobacteria were present in the hay infusion from which 

 the Colpidium came, and in normal oxygenated water these were ingested 

 and digested. Under anaerobic conditions with HoS, they remained alive 

 in the vacuoles; and Liebmann believed that through their assimilating 

 activity in the presence of light, H^S is reduced in amount, and energy 

 is contributed to the ciliate. After reserve glycogen is used up, the bac- 

 terial vacuoles may be attacked by digestive processes, and the ciliates 

 die soon thereafter. 



In many other sapropelic ciliates, Liebmann (1936b, 1937) found, 

 together with dead bacteria, large numbers of living bacteria. These were 

 either packed together in parallel arrangement in bundles [Me to pus) 

 or distributed in the cytoplasm [Chaenia). After a time these symbionts 

 may be digested, and the loss is made up by taking in new saprophytes. 

 When this is prevented, and all symbionts are used in nutrition, the 

 ciliates perish, in spite of filled food vacuoles. Certain living bacteria 

 are therefore necessary for the ciliates' continued life, under existing 

 anaerobic conditions with hydrogen sulphide. In this connection Lieb- 

 mann suggested that the bacteria split off oxygen, which the ciliates 

 use. 



