Semi-Centennial Volume. 97 



modification of parts through use or disuse. Osborn describes the Zeug- 

 lodon, which became dog-like after having been a tree-inhabiting animal ; 

 later it took to the water and became a fish-like, and later an eel-like 

 mammal. 



Whenever a need continues for many years animals not overspecialized 

 against it will modify their anatomy to meet the need, even if it takes a 

 million years or more to do so. Osborn says that all the radiating de- 

 scendants of a group of hornless mammals may at different periods of 

 geologic time give rise to similar horny outgrowths upon the forehead. 

 The horny outgrowths were long needed for self-defense, and in time 

 they came. Natural selection helped after the horns appeared, but did 

 not start them or make them grow. 



The examples are almost numberless wherein the needs of the work- 

 ing cells of the body are impressed on -the cromatin of the egg and sperm 

 cells, and the fertilized egg cell has reacted and made provision to meet 

 the need in the course of milleniums of time, but how was the knowledge 

 of the need transferred to the cromatin of the egg and sperm cells? The 

 fact of the transferal is demonstrated; the method of transfer is not 

 understood with certainty. 



Several ductless glands, such as the pituitary body at the base of the 

 brain, the thyroids, parathyroids and thymus glands of the neck, and 

 the suprarenals on the kidneys, all have a marked influence in stimulat- 

 ing or retarding- the growth of various parts of the body through matter 

 added to or subtracted from the blood. Various glands with ducts, such 

 as the pancreas, liver and reproductive glands, share with the ductless 

 glands the power to send accelerators or restrainers through the blood 

 to various parts of the body. When the pituitary body is injured in a 

 young mammal, such as a dog or sheep, the animal is dwarfed in size, 

 has an excessive development of adipose tissue, and has a delayed or 

 imperfect sexual development. When the same gland is stimulated by 

 disease, unusual growth of various parts of the body takes place. All 

 have observed the remarkable results which have followed the castration 

 of young males, and similar modifications of the development of various 

 parts of the body follow the extirpation of the other glands mentioned. 



It is certain that the blood receives from the cells of these glands 

 certain tiny bodies which produce the effects named. Some of these 

 particles, named antibodies, confer immunity to germ diseases; others, 

 named hoiTnones, stimulate the growth of distant organs; and still others, 

 named chalones, depress, retard or inhibit the activity of distant parts. 



Jordan says that the germ causing influenza is '/^.-oo nim. by li,mo mm. 

 in size, and the germ of infantile paralysis, measuring i/f,ooo mm., is on 

 the limit of microscopic vision. Beyond these, according to Jordan, are 

 the ultramicroscopic bacteria, beyond the range of vision, some of which 

 can pass through a porcelain filter. 



If one-celled plants can be beyond the range of microscopic vision, is it 

 any wonder that tiny messengers sent out by the chromatin of gland 

 cells, or any other cells of the body, should escape observation? These 

 messengers may be poured into the blood by any overworked cell and 



7— Acad. Sci.— 2199 



