254 THE INDUCTIONS OF BIOLOGY. 



by sundry observers, that the microsomes often form rows, 

 held together by intervening substance, seems to imply that 

 these minute bodies are not inert. Leaving aside unsettled 

 questions, however, one fact of significance is manifest — an 

 immense multiplication of surfaces over which inter-action 

 may take place. Anyone who drops into dilute sulphuric 

 acid a small nail and then drops a pinch of iron filings, will 

 be shown, by the rapid disappearance of the last and the long 

 continuance of the first, how greatly the increasing of sur- 

 faces by multiplication of fragments facilitates change. The 

 effect of subdivision in producing a large area in a small 

 space, is shown in the lungs, where the air-cells on the sides 

 of which the blood-vessels ramify, are less than 1/1 00th of 

 an inch in diameter, while they number 700,000,000. In 

 the composition of every tissue we see the same principle. 

 The living part, or protoplasm, is divided into innumerable 

 protoplasts, among which are distributed the materials and 

 agencies producing changes. And now we find this principle 

 carried still deeper in the structure of the protoplasm itself. 

 Each microscopic portion of it is minutely divided in such 

 ways that its threads or septa have multitudinous contacts 

 with those included portions of matter which take part in its 

 activities. 



Concerning the protoplasm contained in each cell, named 

 by some cytoplasm, it remains to say that it always includes a 

 small body called the centrosome, which appears to have a 

 directive function. Usually the centrosome lies outside the 

 nucleus, but is alleged to be sometimes within it. During 

 what is called the " resting stage,^' or what might more pro- 

 perly be called the growing stage (for clearly the occasional 

 divisions imply that in the intervals between them there has 

 been increase) the centrosome remains quiescent, save in the 

 respect that it exercises some coercive influence on the pro- 

 toplasm around. This results in the radially-arranged lines 

 constituting an " aster." What is the nature of the coercion 

 exercised by the centrosome — a body hardly distinguishable 



