1 8 GROWTH 



an organism as the slime mold not all of the food materials 

 absorbed are built up into protoplasm j a part of them is de- 

 stroyed, yielding energy for the building process, and their ma- 

 terial constituents are given off by the slime mold in the form 

 of carbon dioxide and water. In motile organisms much of the 

 energy resulting from respiration goes for work, and in warm- 

 blooded animals like man a considerable part goes for the main- 

 taining of body temperatures. The destruction of the food ma- 

 terials in this process of respiration is also a complicated affair 

 as is evident from the scheme on the opposite page arranged by 

 Shaffer. This shows in outline form what probably happens in 

 the destruction of glucose in the body. 



Since growth involves either increase in size or increase in 

 differentiation or both, the measurement of growth should con- 

 sider both of these phases. We can measure increase in size. One 

 way to do this is to measure increase in volume. This is some- 

 times difficult to do and we therefore frequently use one di- 

 mension such as height as a measure of growth. Since increase in 

 size usually involves increase in weight, growth is frequently 

 measured by taking weights. Differentiation, on the other hand, 

 is difficult to express in units. The result is that our measure- 

 ments of growth are usually concerned with one phase of 

 growth, namely, that which involves increase in size or some- 

 thing related to it. Measured by increase in length, the most 

 rapid growth I am acquainted with is that of the Philippine 

 bamboo, which has been reported as growing eighty-two feet 

 in three months, over eight inches a day. Measured by increase 

 in volume or mass, those microscopic plants, the bacteria, and 

 the microscopic animals, the protozoa, grow most rapidly. Un- 

 der favorable conditions bacteria may double their volume in 

 nineteen minutes. Both the rapidity and the total amount of 

 growth are influenced considerably by age, heredity, food, in- 

 cluding the accessory foods (the vitamins), mineral salts, tem- 

 perature, water, light, toxic materials, the development of vari- 

 ous parts of the body, and other factors. 



