MICROSCOPIC FORMS OF VEGETABLE LIFE. 223 



Physical Basis of Life." In its typical state (such as it presents among 

 Rhizopods, 396) it is a semi-fluid, tenacious, glairy substance, resem- 

 bling alike in aspect and in composition the albumen (or uncoagulated 

 * white 7 ) of an unboiled egg. But it is fundamentally distinguished 

 from that or any other form of dead matter, by two attributes, which (as 

 being peculiar to living substances) are designated vital : 1, its power of 

 increase, by assimilating (that is, converting into the likeness of itself, and 

 endowing with its own properties) nutrient material obtained from with- 

 out; 2, its power of spontaneous movement, which shows itself in an 

 extraordinary variety of actions, sometimes slow and progressive, some- 

 times rapid, sometimes wave-like and continuous, and sometimes rhyth- 

 mical with regular intervals of rest. When examined under a sufficiently 

 high magnifying power, multitudes of minute granules are usually seen 

 to be diffused through it; but these do not appear to belong to it, their 

 presence being (so to speak) accidental, depending upon the nature of" 

 the material which is undergoing assimilation. Protoplasm, whether 

 living or dead, has a great power of absorbing water; but the distinction 

 between these two states is singularly marked by its behavior in regard to 

 any coloring matter which the water may contain. Thus, if living 

 protoplasm be treated with a solution of carmine, it will remain un- 

 stained so long as it retains its vitality. But if the protoplasm be dead, 

 the carmine will at once pervade its whole substance, and stain it 

 throughout with a color even more intense than that of the solution; 

 thus furnishing (as was first pointed out by Dr. Beale) a ready means of 

 distinguishing the ( germinal matter ' or protoplasmic component of the 

 Tissues of higher Animals, from the ( formed material' which is the most 

 conspicuous part of their structure (Chap, xx.) 



220. All those minute and simple forms of Life with which the 

 Microscope brings us into acquaintance, essentially consist of particles of 

 protoplasm; each kind having usually a tolerably definite size and shape, 

 and showing (at least in some stage of its existence) something distinctive 

 in its habit of life. And it is rather according to the manner in which 

 they respectively live, grow, and multiply, than on account of any struc- 

 tural peculiarities, that they are assigned to the Vegetable or to the 

 Animal kingdom respectively. It is impossible, in the present state of 

 our knowledge, to lay down any definite line of demarcation between the 

 two Kingdoms; since there is no single character by which the Animal 

 or Vegetable nature of any organism can be tested. Probably the one 

 which is most generally applicable among those that most closely approx- 

 imate to one another, is not, as formerly supposed, the presence or 

 absence of spontaneous motion; but, on the one hand, the dependence of 

 the organism for nutriment upon organic compounds already formed, 

 which it takes (in some way or other) into the interior of its body; or, 

 on the other, its possession of the power of producing the organic com- 

 pounds which it applies to the increase of its fabric, at the expense of 

 the inorganic elements with which it is supplied by Air and Water. The 

 former, though perhaps not an absolute is a general characteristic of the 

 Animal kingdom; the latter, but for the existence of which Animal life 

 would be impossible, is certainly the prominent attribute of the Vege- 

 table. We shall find that the Protozoa (or simplest Animals, Chaps, x., 

 xi.) are supported as exclusively either upon other Protozoa or upon 

 Protophytes, as are the highest Animals upon the flesh of other Animals 

 or upon the products of the Vegetable kingdom; whilst Protophytes, in 

 common with the highest Plants, draw their nourishment from the 



