716 HANDBOOK OF PHYSIOLOGY. 



the embryo can exhibit any sign of life. It would be quite as impossible 

 for the germ to begin life without external force as without a supply of 

 nutrient matter. Without the force wherewith to take it, the matter 

 would be useless. The heat, therefore, which in conjunction with moist- 

 ure is necessary for the beginning of life, is partly expended as chemical 

 power, which causes certain modifications in the nutrient material sur- 

 rounding the embryo, e. g., the transformation of starch into sugar in 

 the act of germination; partly, it is transformed by the germ itself into 

 vital force, whereby the germ is enabled to take up the nutrient material 

 presented to it, and arrange it in forms characteristic of life. Thus the 

 force is expended, and thus life begins when a particle of organized 

 matter, which has itself been produced by the agency of life, begins to 

 transform external force into vital force, or in other words into a power 

 by which it is enabled to grow and develop. This is the true beginning of 

 life. The time of birth is but a particular period in the process of de- 

 velopment at which the germ, having arrived at a fit state for a more 

 independent existence, steps forth into the outer world. 



The term "dormant vitality," must betaken to mean simply the 

 existence of organized matter with the capacity of transforming heat or 

 other force into vital or growing power, when this force is applied to it 

 under proper conditions. 



The state of dormant vitality is like that of an empty voltaic battery 

 or a steam-engine in which the fuel is not yet lighted. In the former 

 case no electric current passes, because no chemical action is going on. 

 There is no transformation into electric force, because there is no chemi- 

 cal force to be transformed. Yet, we do not say, in this instance, that 

 there is a store of electricity laid up in a dormant state in the battery; 

 neither do we say that a store of motion is laid up in the steam-engine. 

 And there is as little reason for saying there is a store of vitality in a 

 dormant seed or ovum. 



Next to the beginning of life, we have to consider how far its con- 

 tinuance by growth and development is dependent on external force, and 

 to what extent correlated with it. 



Mere growth is not a special peculiarity of living beings. A crystal, 

 if placed in a proper solution, will increase in size and preserve its own 

 characteristic outline ; and even if it be injured, the flaw can be in part 

 or wholly repaired. The manner of its growth, however, is very differ- 

 ent from that of a living being, and the process as it occurs in the latter 

 will be made more evident by a comparison of the two cases. The in- 

 crease of a crystal takes place simply by the laying of material on the 

 surface only, and is unaccompanied by any interstitial change. This is, 

 however, but an accidental difference. A much greater one is to be 

 found in the fact that with the growth of a crystal there is no decay at 

 the same time, and proceeding with it side by side. Since there is no life 



