VITAL PROPERTIES AND STIMULANTS. l6l 



is placed in the body of the funnel, and the mouth 

 immersed in water ; mercury is poured into the open 

 extremity of the tube, and ascends in the other stem 

 until it meets the fluid in the funnel. So soon as the 

 endosmose commences, the rising fluid pushes the mer- 

 cury before it ; and the amount of the force by which 

 this is effected, is ascertained by pouring in more mer- 

 cury until the further rise of the fluid is checked. The 

 height of the column of mercury affords an estimate of 

 the pressure of the ascending fluid, which is of course 

 due to the force of the endosmose. In this way it may 

 be shown, that a syrup three times the density of water 

 produces an endosmose capable of sustaining a pressure 

 equal to the weight of three atmospheres. 



(145.) Vital Properties. After abstracting all that 

 can reasonably be allowed to the physical properties of 

 the tissue, arid to the chemical or other effects which 

 operate in modifying every vital phenomenon, whatever 

 still remains unaccounted for in the functions of ve- 

 getation, must be ascribed to the direct operation of the 

 vital force itself. What life is, whether it is a simple 

 quality, the effects of which are variously modified ac- 

 cording to the nature of the tissue in which it resides, 

 and by means of which it acts, or whether it possesses 

 several distinct properties, which are severally capable of 

 acting only upon and through particular tissues, is quite 

 unknown to us. For the sake of convenience, and pro- 

 visionally merely, the physiologist considers animal life 

 to be compounded of certain properties, and that its 

 various functions are performed by these properties, 

 acting through the intervention of different kinds of 

 tissue. There are three of these properties attached to 

 animal life, which may be styled respectively its ex- 

 citability, irritability, and sensibility. 



(146.) Excitability. The excitability of animal life, 

 which is also termed the " vis formativa," is manifested 

 through the cellular tissue, by which the function of 

 nutrition is carried on ; it is that property by which 

 this tissue takes cognizance of the action of external 



