PROTOZOA AND OTHER ANIMALS 985 



for total nitrogen were used. Mangold (1933) accepted the estimate that 

 the ciliates provide about one percent of the protein used daily and, 

 under certain circumstances, from 2 to 3 percent. C. Schwarz (1925), 

 however, thought it probable that the greater part of the protein 

 requirements are met by the microorganisms; and Dogiel and Wino- 

 gradowa-Fedorowa (1930), as well as Westphal (1934a), considered 

 the daily reproductive rate to be much higher than 7 percent. 



The conclusion that the ciliates are mutualists, participating in the 

 protein economy of the host, was deduced by Ferber (1928, 1929a) 

 from the observed fact that the population density increases at the time 

 of growth, reproduction, and lactation. He himself, like Mowry and 

 Becker (1930), attributed the increase to the increased nutrition and 

 especially to larger protein supply; but, as the latter authors pointed out, 

 the facts do not warrant the deduction. 



Ferber pursuing the ideas advanced by C. Schwarz (1925), sug- 

 gested that the role of the ciliates may be transformation of the protein 

 in the plant food into easily digestible animal protein, and that in 

 times of increased protein need by the host, this activity is enhanced 

 by additions to the ciliate population. The result, of course, would be 

 an increased ratio of ciliate nitrogen to total nitrogen. Becker, Schulz, 

 and Emmerson (1930) remarked that although it is an observed fact 

 that such protein transformations take place, and ciliates are eventually 

 digested, it is doubtful if this substantially benefits the host. 



Mangold (1933) recognized usefulness to the host, in the mechani- 

 cal role of the ciliates in mixture and trituration of the rumen contents, 

 a role which had been suggested by Bundle (1895), Scheunert (1909), 

 and Dogiel (1925). Conclusive evidence that there is any essential aid 

 to the digestive processes in the mechanical activities of the ciliate is, 

 however, lacking. 



It has been found that cattle will develop and reproduce normally on 

 a diet that will produce symptoms of vitamin B (B^) deficiency in other 

 animals. It has therefore been believed that vitamins of the B complex 

 are synthesized within the alimentary tract of ruminants, and the micro- 

 organisms have been investigated in this connection. Bechdel, Honey- 

 well, Dutcher, and Knutsen (1928) found evidence of synthesis of the 

 B complex by bacteria, as others have also reported. Manusardi (1933) 

 investigated the possibility of synthesis of the vitamin (antiberiberic) 



