21 



o 



lhat are nourished like plants, this is the case of all ani- 

 mals, whether oviparous or viviparous, whilst they are 

 inclosed in the egg, or in the belly of their mother : the 

 umbilical vessels may be considered in the egg, or fn the 

 matrix, as roots which imbibe the nourishment. It is 

 the same with respect to insects that multiply "by shoots \ 

 whilst the young one still adheres to its mother, it is 

 nourished in a manner little different from that which is 

 peculiar to branches. Animal grafts nearly resemble 

 vegetable in this particular. 



Lastly : The skin of the human body imbibes, like 

 the leaves of plants, the vapours with which the air 

 abounds ; and although men draw in much less nourish- 

 ment by this means than vegetables, it is, nevertheless, 

 true, that their skin and leaves have, in regard to this 

 circumstance, a great affinity to each other. Perhaps 

 >ve may be able, some time or other, to discover ani- 

 mals which are nourished by their skin only, as certain 

 plants are by their leaves. 



28. Do we then in vain seek for a peculiar character 

 whereby we may distinguish the vegetable from the ani- 

 mal 1 I perceive a new property, which will, perhaps^ 

 furnish us with what we seek for. 



A muscular fibre contracts of itself on the touch of all 

 bodies, whether solid or liquid : this property is known 

 by the name of irritability. It has nothing in it com- 

 iiiuii to sensibility : the parts which are most sensible 

 are not irritable, and the parts which are most irritable 

 are not sensible. Neither ought we to confound irrita- 

 bility with elasticity : a dry fibre is very elastic, and not 

 at all irritable. Animals purely gelatinous are not 

 elastic, and are, notwithstanding, very irritable. In 

 short, the fibres of old men, though much more elastic 

 than tliose'of infants, are much less irritable. 



We have seen that the heart is a real muscle. If we 

 extract it from the breast, it will continue to move till 



