The Intimate Causes of Old Age. 193 



general conclusion that the vital coefificient of the organic 

 life, which in theory should be biostatic, is thus slowly 

 diminished to a point where the personal life succumbs to 

 almost any fresh attack from without, or new insurrection 

 within. For certain disease germs become intrenched in 

 the tissues, so to speak, and there bide their time to deliver 

 further assaults, and go on forays up and down the blood 

 circulatory. Moreover, the roaming white cells or cor- 

 puscles of the blood sometimes assume the- role of intra- 

 organic assailants ; — and this brings us to consider one of 

 the latest theories of old-aging, that of Prof. Elie Metch- 

 nikoff, of the French Institute, namely, that after middle 

 age, these leucocytes, now known as phagocytes, begin to 

 prey on the more highly differentiated cells of the stable 

 tissues, bone, muscle, skin, etc., and even on the neurons 

 of the brain and cord, to the extent that a gradual wasting 

 away ensues, with the consequent phenomena of old age. 



Professor Metchnikoff distinguishes two classes of 

 phagocytes, the macrophages and microphages, the latter 

 smaller than the former, having extensible nuclei which 

 permit them to pass freely through all the tissues. It is 

 to the more voracious macrophages, however, which are 

 essentially minute animals, that the damage to the organic 

 tissues in advanced life is chiefly due : they turn cannibals, 

 so to speak, and devour the cells of the associated tissues ; 

 and the cause of this unnatural perversion of appetite, or 

 morale, is attributed to poisons of the nature of ptomaines, 



