1914] Lafayette B. Mendel 161 



ing has hitherto furnished the best measure of the total changes of 

 the body. 



During growth the Compounds and elements of the body are 

 undergoing change and chemical variations. A detailed knowledge 

 of what these are is desirable from many points of view. At the 

 present day only the beginnings in this direction have been made. 

 The work of obtaining statistics as to the varying chemical compo- 

 sition of the component parts of the growing organism at different 

 periods of development involves laborious analyses, with the added 

 difficulty that in order to secure data an experiment must be stopped 

 by the sacrifice of the subject for examination. The correlation in 

 development between different organs and tissues, the appropriate 

 symmetry and interrelation of the parts, the changes in the " körper- 

 gestaltende " as well as the " körpervermehrende " f unction are de- 

 serving of close investigation. The inroad into these and related 

 fields has been begun. 



When the statistics derived from periodic measurements of the 

 continuous changes going on in young animals are expressed in 

 graphic form, the so-called curves of growth are obtained. The 

 fixity of the growth curve for the different species and, in so far as 

 this point has been studied, of the sexes in each species is perhaps 

 the most remarkable phenomenon of growth. " We are aware of no 

 conditions compatible with life in which the general character of the 

 growth curve with its acceleration during adolescence can be altered. 

 Minor variations may, however, arise." Variations in the growth 

 of dififerent individuals are for the most part inborn — inherited 

 fundamental characteristics of the individual. We know of no 

 method or means of altering the peculiarities of growth. Nutrition, 

 which is often looked upon as a Controlling factor, can do no more 

 than give free scope to the inherent tendency to grow. As Rubner 

 has remarked, the hope of altering this tendency is quite as utopian 

 as the attempt to prolong life indefinitely. 



It has already been pointed out that the cells need not be the sole 

 factors involved in the increase of size attending growth. Extra- 

 cellular parts may come into play. Nevertheless the importance of 

 the cells as the material basis of biological phenomena and the seat 

 of physiological functions has tended to center attention upon these 

 histological units in growth. We are brought face to face with the 



