PROTOZOA AND OTHER ANIMALS 975 



The kind of food taken has a striking influence on the cihate popula- 

 tion. Green plant material was regarded as of fundamental importance 

 by Trier (1926), with emphasis on the chlorophyll content. Weineck 

 (1934) expressed agreement with this view, but Westphal (1934b) 

 denied that there is proof of chlorophyll need. In experiments by 

 Mowry and Becker (1930), green fodder alone maintained a low popu- 

 lation. Hay and water alone also maintained a low population, which 

 was more than doubled when cornstarch was added. A much greater 

 increase occurred when a grain mixture, consisting of ground corn, 

 ground oats, wheat bran, and linseed oil meal, was given with hay. 

 There is a limit to this increase, however. Although the densest popula- 

 tion of all was developed on grain alone, there was soon a very great 

 decrease in the number of ciliates. As was pointed out by Mangold 

 (1929), some coarse food is essential. Hay with cornstarch and either 

 plant or animal protein, instead of with grain, also maintained a high 

 level of population density. Apparently in the grain both the starch and 

 the protein constituents are stimulating factors, although the Mangold 

 school has maintained that the protein alone is determinative. 



Other factors influencing the ciliate population of the rumen that 

 have been discussed are density of the contents and pH. Mowry and 

 Becker (1930) could not corroborate the findings of Dogiel and 

 Fedorowa (1929) and Ferber (1929b) that thick rumen contents con- 

 tain relatively more ciliates than thin fluid contents. Mowry and Becker 

 found the average pH in the rumen of goats to be 7.7, with two-thirds 

 from 7.6 to 7.8 and extremes of from 6.7 to 8.2. Within these limits, 

 there seemed to be no notable changes in the ciliate population that 

 could be attributed to the pH itself. Mangold and Usuelli (1930) found 

 the pH of fresh rumen contents of sheep to be from 7.5 to 7.8. 



When the ciliates pass into the omasum, abomasum, and intestine, 

 they are destroyed. As nutriment passes posteriorly from the reticulum, 

 a vast number of ciliates must go with it; it is difficult to conceive of 

 any mechanism by which they could be kept back. The population could 

 be maintained only by an adequate rate of multiplication, going on con- 

 tinuously. The rapid disappearance of the ciliates on starvation of the 

 host probably could not be explained simply by starvation, followed 

 by death of the ciliates in the rumen and reticulum; it is more likely that 

 the rate of reproduction declines, and the passage of ciliates into the third 

 stomach rapidly reduces the population. 



