1 8 NORMAL HISTOLOGY AND ORGANOGRAPHY. 



white of an egg. It differs from all lifeless matter 

 in being able to reproduce itself, repair a wasted or 

 depleted condition, develop, and grow. The sharpest 

 kind of a line divides this living matter from dead 

 matter, and yet we know that the closest relations 

 and interrelations do exist. Even in our own phys- 

 ical bodies these two forms prevail, for the outer 

 layer of the skin, the hair and nails, the liquid part 

 of blood and lymph, the fibers of ligaments and 

 tendons, the lime of bone, all are lifeless or dead 

 matter. While today we firmly believe that living 

 matter develops only from pre-existing living mat- 

 ter, we know that dead matter is constantly and 

 unceasingly being incorporated into living matter, 

 actually transformed into living matter through the 

 mysterious elaboration of this selfsame living sub- 

 stance. Thousands of tons of dead matter are thus 

 daily converted into living matter, throughout the 

 animal and vegetable kingdoms, on land and in the 

 seas. Were this constructive force nature's only 

 process, a most unfortunate condition would soon 

 prevail, with a dearth of the one form and a great 

 surplus of the other the living. But we recognize 

 a reverse current equally strong whereby the "dust 

 shall return to the earth as it was and the spirit to 

 the God who gave it." That mysterious and in- 

 sidious enemy Death is absolutely necessary that 

 man, or any other living being, may live. It is the 

 duty of the medical profession to divert this return 

 current as far as possible that humanity, one and 

 all, may enjoy threescore and ten happy years. 

 Protoplasm, so intimately associated with life, has 



