CHAPTER X 



THE GROWTH OF THE PROTOZOA 



Oscar W. Richards 



Growth is a fundamental attribute of living organisms, manifested by 

 a change of size of the individual, or in the number of organisms in a 

 unit of environment. Negative growth may occur during adverse con- 

 ditions or in certain dimensions when growth involves change of form. 

 The analysis of population growth requires knowledge of the environ- 

 ment, the individuals, and the interactions of each on the other. 



Growth is determined by measurement, and the information gained 

 from any single measure is delimited by the nature of the measuring unit 

 chosen. Rarely is a single measure adequate for the study of growth, 

 even though it may be useful for practical application. Analytical studies 

 require the simultaneous use of as many different measures as are neces- 

 sary to give a picture sufficiently complete for the analysis. When there 

 is no change in form, certain dimensions may be related directly, as 

 length with volume or weight, but in allometric growth the conversion 

 constants may change during the course of the growing period. These 

 problems will be illustrated and discussed in this chapter, in so far as 

 numerical data are available. 



Methods for the Measurement of Growth 



Individual Protozoa have been measured to show growth changes in 

 length and breadth, but these two dimensions may not permit very exact 

 calculation of volume if the shape of the animal departs much from 

 that of a sphere, cube, ellipsoid or other simple geometrical form. The 

 area of the animal may be calculated by the use of a planimeter, from 

 an enlarged photomicrograph or a tracing of the outline of the animal. 

 The softer animals may be gently compressed between a slide and a 

 cover glass, and the area measured. Multiplication of this figure by 

 that of the thickness of the preparation gives the volume. The three- 

 halves power of the area obtained from planimetric measurement may 



