The Intimate Causes of Old Age. 201 



highly rectified particles go to the cells of the nobler tis- 

 sues and orjrans. 



In an adolescent organism, normal, healthy, and strong, 

 this eliniinative process is practically adequate. Adventi- 

 tious substances are expelled or broken down and resolved 

 chemically. 



But in older organisms, during periods of weakened 

 action, the process of resolution is less complete ; micro- 

 scopic dirt may accumulate in enfeebled cells. If not 

 dirt, what is that darker-tinted residuum in old proto- 

 plasm ? 



Is there dirt in the blood ? Or rather, to how great an 

 extent is the blood a dirty liquid? In other words, is 

 dirt taken up, associated with nutritious particles, by the 

 absorbents and lacteals ? 



We know that the fine particles of inorganic substances, 

 administered as medicines and poisons, pass readily into 

 the blood, and speedily enter the protoplasm of brain and 

 muscle cells. In the examination of old amoebse, which 

 are nourished in dirty water, we see a great deal of this. 

 Under high power the same is discernible in a culture of 

 bacteria which can be killed out by an admixture of dirt 

 in the fluid. 



It is not of the chemical action of inorganic particles in 

 the protoplasm of the cells that we are here treating, how- 

 ever, but of their merely negative behavior, or presence 

 as dirt. A particle of arsenic, antimony, or iron may ex- 



