36 THE DATA OF BIOLOGY. 



while itself undergoing molecular changes, will convert 100 

 parts of sugar into alcohol and carbonic acid ; and during its 

 own decomposition, one part of diastase " is able to effect the 

 transformation of more than 1000 times its weight of starch 

 into sugar." As illustrations of the second species, 



may be mentioned those changes which are suddenly produced 

 in many colloids by minute portions of various substances 

 added to them — substances that are not undergoing any 

 manifest transformation, and suffer no appreciable effect 

 from the contact. The nature of the first of these two 



kinds of communicated molecular change, which here chiefly 

 concerns us, may be rudely represented by certain visible 

 changes that are communicated from mass to mass, when a 

 series of masses has been arranged in a special way. The 

 simplest example is that furnished by the child's play of 

 setting bricks on end in a row, in such positions that when 

 the first is overthrown it overthrows the second ; the second, 

 the third ; the third, the fourth ; and so on to the end of the 

 row. Here we have a number of units severally placed in 

 unstable equilibrium, and in such relative positions that each, 

 while falling into a state of stable equilibrium, gives an im- 

 pulse to the next, sufficient to make the next, also, fall from 

 unstable to stable equilibrium. Now since among mingled 

 compound atoms, no one can undergo change in the arrange- 

 ment of its parts without a molecular motion that must cause 

 some disturbance all around ; and since an adjacent atom 

 disturbed by this communicated motion, may have the arrange 

 ment of its constituent molecules altered, if it is not a stable 

 arrangement ; and since we know, both that the atoms which 

 are changed by this so-called catalysis are unstable, and that 

 the atoms resulting from their change are more stable ; it 

 seems probable that the transformation is really analogous, 

 in principle, to the familiar one named. "Whether thus 

 interpretable or not, however, there is great reason for think- 

 ing that to this kind of action, is due a large amount of vital 



