

316 HOW TO WORK 



mass has divided into several, and in fig. 364 these are set free, 

 and being now freely supplied with pabulum, in consequence of 

 the absence of the thick layer of formed material upon their 

 surface, as in figs. 358 to 360, they grow and multiply rapidly. 

 Such are the changes which are considered to result from what 

 is called " irritation," and which constitute the essential phenomena 

 of " inflammation." In irritation, the access of pabulum to 

 germinal matter is facilitated, because the protective external 

 covering of formed material is removed or rendered more per- 

 meable by chemical or mechanical means. This is, I believe, 

 the real action of the so-called chemical and mechanical irritants.* 

 It is, therefore, better not to employ the term irritation at all. 

 Although all medical writers have freely used this word, no one 

 has been able to explain exactly what he means by it. 



The above view is capable of wider application. Heat 

 acts as a "stimulus" to the development of the embryo chick, 

 simply by facilitating the access of pabulum to the germinal 

 matter of the living embryo. The heat does not become the life, 

 for the life is there; but it is simply one of the conditions 

 necessary for the manifestation of this mysterious active power. 

 Without the influence of heat, the pabulum cannot get through 

 the formed material to the already living germinal matter; but as 

 formed material is expanded, and the permeating properties of 

 the surrounding nutrient fluids increased by heat, the pabulum 

 comes rapidly into contact with the living particles, which commu- 

 nicate to it the same wonderful power they already possess. 



In the examples already adduced, the formation of the formed 

 material takes place upon the outer part of the germinal matter, and 

 as the cell increases in size the layers, first formed, are pushed out 

 by those last produced. In many instances, however, formed mate- 

 rial of another kind is deposited amongst the particles of germinal 

 matter. In pi. XXXVIII, figs. 239, 240, are represented some of the 

 young starch-holding cells of the potato. The so-called cell-wall is 

 formed around the germinal matter, while the starch is deposited as 

 small insoluble particles in its substance. In fact by the death of par- 

 ticles upon the surface of the living matter, the cellulose 'cell-wall' is 

 formed, while, as a consequence of a similar change affecting the par- 

 ticles further inwards, starch results. In some of the cells no starch is 

 found in the interior, but instead, the wall of the cell is greatly 

 thickened by the deposition of a closely allied material upon its 

 internal surface, layer within layer. 



* See a lecture on " First Principles." Dublin Medical Press, 1863. 



