498 Minnesota Plant Life. 



the living substance, irritable phenomena arc related with past 

 time as well as with the present. Here, indeed, lies one of the 

 principal differences between a livino- thing and an insentient 

 mechanism composed of springs, wheels, pulleys, levers and 

 rods. One has a past ; the other is a creature of the present. 



Irritable behavior of living substance. While all manifes- 

 tations of irritability must be attributed to responses by the 

 living substance, it is convenient to examine first those responses 

 made by living substance, as such; and later to consider the irri- 

 table responses of cells and organs. A further distinction may be 

 made, for purposes of analysis, between induced and automatic 

 responses. Really, all responses are induced by stimuli ; but 

 if these stimuli originate witliin the living substance — as a result 

 of subtle rearrangements of its component structure — the re- 

 sponses may then be termed automatic, in contradistinction to 

 responses which are plainly induced by external stimuli. Thus, 

 the extraordinary marshalling into groups of the component 

 parts of a mass of living substance, before division of a cell 

 takes place, w'ould be termed automatic ; the lashing of a swim- 

 ming thread, such as that of a spermatozoid, is also automatic; 

 but the contraction of a portion of protoi)lasm when exposed 

 to a slight electric shock would be regarded not as automatic 

 but as induced. 



Examples of automatic irritable phenomena in living sub- 

 stance are very numerous. 1 Icre should be classified the stream- 

 ing movement, the lashing movement, the crawling movement, 

 and the spontaneous contractions of protoplasm. Here, too, 

 should be grouped those amazing evolutions by wdiich the 

 nucleus of a cell divides itself into two, prior to cell division. 

 It is by no means a mere halving of the nucleus that then 

 takes place ; Init a complex segregation of certain portions on 

 one side and certain portions on the other side of a neutral line, 

 the whole recalling military marchings and countcrmarchings, 

 or the working of some ingeni(nis manufacturing contrivance, 

 such as the pressroom of a metropdlit.in newspaper. Automatic 

 movements are dependent upon suitable outward conditions, — 

 as are also induced movements. Thus, ton high or too low a 

 temi)eratin-e, too strong or too weak iiluniinatiDU, or some 

 other condition of the environment. in;iy pre\ent their appear- 



