1 6 ELEMENTS OF BIOLOGY. 



ing, of a very high grade of organisation. They possess a 

 mouth, masticatory organs, a stomach, and aHmentar)'- canal, 

 a distinct and well-developed nervous system, a differen- 

 tiated reproductive apparatus, and even organs of vision. 

 Repeated experiments, however, have shown the remarkable 

 fact, that, with their aquatic habits and complex organisa- 

 tion, the Rotifers are capable of submitting to an apparently 

 indefinite deprivation of the necessary conditions of their 

 existence, without thereby losing their vitality. They may 

 be dried and reduced to dust, and may be kept in this state 

 for a period of many years ; nevertheless, the addition of a 

 little water will, at any time, restore them to their pristine 

 vigour and activity. It follows, therefore, that an organism 

 may be deprived of all power of manifesting any of the 

 phenomena which constitute what we call life, without los- 

 ing its hold upon the vital forces which belong to it. It 

 seems, however, hardly necessary to add that this is a mere 

 instance of revival and not of revitalisation. The desiccated 

 Rotifers are not truly dead, but are merely in a state of sus- 

 pended animation. % 



USE OF THE TERM VITAL FORCE. 



If, in conclusion, it be asked whether the term ''vital 

 force " is any longer permissible in the mouth of a scientific 

 man, the question must, I think, be answered in the affirma- 

 tive. Formerly, no doubt, the progress of science was 

 retarded and its growth checked by a too exclusive reference 

 of natural phenomena to a so-called vital force. Equally 

 unquestionable is the fact that the development of Biological 

 science has progressed contemporaneously with the succes- 

 sive victories gained by the physicists over the vitalists. 

 Still, no physicist has hitherto succeeded in explaining any 

 fundamental vital phenomenon upon purely physical and 

 chemical principles. The simplest vital phenomenon has 

 in it something over and above the merely chemical and 

 physical forces which we can demonstrate in the laboratory. 



