1914] Lafayette B. Mendel 159 



cells, enlargement of cells, and deposition of intercellular substance, 

 the first two being the most potent of all. Increase in the number 

 of cells is largely, although not wholly, an embryonic phenomenon ; 

 increase in the size of cells and deposition of intercellular substance 

 are especially important from the later embryonic period through 

 the time of birth and up to the cessation of body-growth. The 

 most obvious result of the growth of the cells, the tissues, and the 

 Organs, is growth or increase in size of the body." 



If organisms are composed of both living matter and formed 

 substance, it is evident that a growth may result from the increase 

 of volume of either of these. This viewpoint is somewhat broader 

 than that which governs the usual attitude of the physiologist. If 

 body weight is taken as the measure of growth, it may be pro- 

 nouncedly altered by deposition or removal of reserve materials, 

 such as glycogen and fat, as well as by the retention of water and 

 other products. In the narrower and stricter sense this is not 

 growth. In many individuals the end of growth, as the physiolo- 

 gist intends to apply the term, is reached long before the gain in 

 body weight ceases to manifest itself. Real growth in man, for 

 example, usually is considered to stop at an age of 25 to 30 years 

 when body length has reached its maximum. Many individuals 

 continue to gain in weight and size until they are 50 years old ; but 

 this is of quite a different order than the gains in earlier years. 



All of these considerations — cell division, increase in number or 

 volume of cells, etc. — fail to take into consideration some of the 

 most striking features of growth as it applies to the higher organ- 

 isms. Perfect growth and development implies a far reaching cor- 

 relation of the various parts of the body. An upset in this nicely 

 balanced relationship is speedily recognized as an anomaly. Energy 

 and matter are insufficient to explain the consummation and main- 

 tenance of a normal as contrasted with an abnormal composition of 

 the cells. The specificity of growth is something marked, particu- 

 larly when we contrast the normal with perverted growth. The 

 regularity and characteristic individuality of the ontogenetic devel- 

 opment Seen in each species has found expression in the explicit defi- 

 nition by Schloss : "So können wir das normale Wachstum eines 

 jeden Organismus auffassen als artspezifische korrelative Vermehr- 

 ung der Körpermasse in bestimmten Zeitabschnitten." The corre- 



