314 PRINCIPLES OF SOIL MICROBIOLOGY 



flagellum is present, one or more may be directed backward. Some low flagel- 

 lates can form pseudopodia. 



3. Ciliata or Infusoria, motility by means of numerous cilia or short hair-like 

 processes present during the entire existence of the protozoa or during their 

 embryonic stage only. The cilia are either evenly distributed over the surface 

 of the organisms or are restricted to certain regions. Large spine-like cirri or 

 setae, or vibrating membranelles may be formed from fusion of cilia. Most are 

 free swimming, some are attached by rigid or flexible stalks or pedicels. 



4. Sporozoa, motility reduced by parasitism. 



The soil forms are found among the first 3 general groups. 



Physiology of protozoa. The physiology of the protozoa cannot be 

 studied adequately, in a manner similar to higher organism or to micro- 

 scopic plant organisms, as fungi, bacteria and algae. This is due largely 

 to the fact that they cannot be cultivated yet in pure cultures, free 

 from bacteria. An approach in this direction has been made by the 

 cultivation of protozoa with single species of bacteria. 



Most of the protozoa are aerobic, obtaining their oxygen, necessary 

 for oxidation purposes, from the air by absorbing it through the permea- 

 ble membrane, without the aid of specialized respiratory organs. A 

 few forms are anaerobic, obtaining the oxygen by reduction of oxygen 

 rich substances. Oxidation is closely associated with nutrition and is 

 followed by the excretion of the waste products, such as C0 2 , urea and 

 other products of metabolism. 



The optimum temperature for the development of protozoa is 18- 

 22°C. Excessive heat kills the protozoa, but excessive cold does not 

 injure them beyond retarding their vital activities. 



The optimum reaction for the activities of protozoa was at first be- 

 lieved to be at the neutral point. Good growth was also obtained in 

 acid media. 9 The limiting acid and alkaline reaction values for the 

 growth of Paramoecium caudatum were found to be at pH 5.0 and 9.0 ; 10 

 in other experiments Paramoecium was reported to develop normally at 

 pH 6.4 to 8.0; beyond these limits, development is restricted and en- 

 cystment may take place. Various soil ciliates, flagellates and amoebae 

 were found to be able to live and reproduce in artificial media even at 



9 Vahlkampf. Beitrilge zur Entwicklungsgeschichte von Amoeba Umax, 

 einschliesslich der Ziichtung auf ktinstlichen Nahrboden. Arch. Protistenk., 

 6: 167. 1905. 



10 Dale, D. On the action of electrolytes on Paramoecium. Jour. Physiol., 

 46: 129-140. 1913; Koffman, M. tJber die Bedeutung der Wasserstoffionen- 

 konzentration fur die Encystierung bei einigen Ciliatenarten. Arch, mikrosp. 

 Anat. Entwicklungs., 103: 168-181. 1924. 



