110 LAY SERMONS, ESSAYS, AND REVIEWS. [vu. 



in it and give it its colour, a comparatively small number of 

 colourless corpuscles, of somewhat larger size and very irregular 

 shape. If the drop of blood be kept at the temperature of the 

 body, these colourless corpuscles will be seen to exhibit a mar 

 vellous activity, changing their forms with great rapidity, draw 

 ing in and thrusting out prolongations of their substance, and 

 creeping about as if they were independent organisms. 



The substance which is thus active is a mass of protoplasm, 

 and its activity differs in detail, rather than in principle, from 

 that of the protoplasm of the nettle. Under sundry circum 

 stances the corpuscle dies and becomes distended into a round 

 mass, in the midst of which is seen a smaller spherical body, 

 which existed, but was more or less hidden, in the living cor 

 puscle, and is called its nucleus. Corpuscles of essentially 

 similar structure are to be found in the skin, in the lining of 

 the mouth, and scattered through the whole framework of the 

 body. Nay, more ; in the earliest condition of the human 

 organism, in that state in which it has but just become distin 

 guishable from the egg in which it arises, it is nothing but an 

 aggregation of such corpuscles, and every organ of the body was, 

 once, no more than such an aggregation. 



Thus a nucleated mass of protoplasm turns out to be what 

 may be termed the structural unit of the human body. As a 

 matter of fact, the body, in its earliest state, is a mere multiple 

 of such units ; and, in its perfect condition, it is a multiple of 

 such units, variously modified. 



But does the formula which expresses the essential structural 

 character of the highest animal cover all the rest, as the state 

 ment of its powers and faculties covered that of all others ? 

 Very nearly. Beast and fowl, reptile and fish, mollusk, worm, 

 and polype, are all composed of structural units of the same 

 character, namely, masses of protoplasm with a nucleus. There 

 are sundry very low animals, each of which, structurally, is a 

 mere colourless blood-corpuscle, leading an independent life. 

 But, at the very bottom of the animal scale, even this simplicity 

 becomes simplified, and all the phenomena of life are manifested 



