THE CILIATES 



361 



positive diplococci and other bacteria on 

 different occasions. Sugden and Oxford 

 (1955) found that a "pure", washed, living 

 suspension of Metadiniiun ivediuni had no 

 action on glucose in the Warburg apparatus. 



Diplodlnium and related species were 

 found by Hungate (1946) to produce hydro- 

 gen, carbon dioxide and volatile acids. 



The skeletal plates of all ophryoscol- 

 ecids which have them stain brown with 

 iodine and are polysaccharide in nature. 

 According to Oxford (1955), Hirst et al. 

 extracted enough of the storage polysac- 

 charide from Metadinium medium to 

 identify it as of the "glycogen-amylopectin" 

 type, but they were not sure whether it 

 was pure amylopectin. 



The mode of nutrition of Ophryoscolex 

 has not been determined, altho it is known 

 to ingest starch granules and sometimes 

 cellulose fibers. 



Lubinsky (1957b) reported that acci- 

 dental predation on smaller protozoa is a 

 common trait of many of the larger spe- 

 cies of Ophryoscolecidae, particularly of 

 Diplodinium and related cellulose-feeding 

 genera. Predation is rare in Ophryosco- 

 lex, however. The prey of these occa- 

 sional predators consists primarily of 

 spineless smaller species. The spines 

 are thus of value in protecting the smaller 

 ophryoscolecids against ingestion. Lubin- 

 sky gave a table listing cases of predation 

 among ophryoscolecids from the Canadian 

 reindeer, goat, sheep and Indian water 

 buffalo, which included 8 genera and 9 

 species of predators and 7 genera and 9 

 species of prey. 



The role of the rumen protozoa in 

 their host's nutrition is still not clear. 

 Young animals on a milk diet do not have 

 them. As they grow older and begin to 

 feed on hay and grass, they become in- 

 fected from protozoa in the saliva of 

 faunated animals. This is the only way in 

 which transmission occurs. There are 

 no resistant forms or cysts, and the pro- 

 tozoa are killed when they enter the 

 abomasum. 



The relation between the protozoa and 

 their hosts is not symbiotic, since the host 

 does not need the protozoa for survival, 

 and indeed gets along perfectly well without 

 them. Becker, Schulz and Emmerson 

 (1929, 1930) and Winogradow et al. (1930) 

 killed the protozoa in the rumens of goats 

 without harming the goats. The defaunated 

 animals continued to break down cellulose 

 just as actively as the normal controls, due 

 to the action of cellulolytic bacteria. 

 Pounden and Hibbs (1950) raised calves 

 successfully without protozoa. 



The fact that defaunation is not harm- 

 ful does not mean, however, that the pro- 

 tozoa are of no value to their hosts. It 

 means simply that they are not essential. 



It has been suggested that the protozoa 

 might harm their hosts by excreting am- 

 monia which may then not be utilized by 

 the rumen bacteria for protein synthesis 

 and which would therefore be lost to their 

 hosts; by robbing the host of B vitamins; 

 by feeding on and destroying valuable bac- 

 teria; or by producing lactic acid and other 

 undesirable intermediate products of car- 

 bohydrate metabolism which the rumen 

 bacteria cannot cope with (see Oxford, 

 1955). However, there is no proof that 

 they are actually harmful, and this is sim- 

 ply speculation. 



Rumen protozoa form about 20% of the 

 protein which reaches the abomasum 

 (Hungate, 1955). McNaught et al. (1954) 

 found that the rumen protozoan and bacter- 

 ial proteins both had a biological value for 

 rats of 80 to 81, which is higher than that 

 of brewer's yeast (72). Furthermore, the 

 true digestibility of the protozoan protein 

 was 91%, much higher than that of the bac- 

 terial (74%) or yeast (84%) proteins. Hence 

 the protozoan protein is nutritionally su- 

 perior. No amino acid analyses have been 

 carried out on it. 



While many of the protozoa store re- 

 serve starch (amylopectin), this stored 

 starch is not of much importance for the 

 host's nutrition. About 1% of the carbohy- 

 drate required by a mature sheep is sup- 

 plied from this source (Hungate, 1955). 



