22 INTRODUCTION TO 



in many of their operations and actions, they would appear to be 

 so nearly allied as to make it reasonable to suppose that it was 

 possible, even probable, for them to be composed of the same mate- 

 rials. But these actions are not sufficient for us to form oiu' judg- 

 ment upon [this question] ; we must take every circumstance into the 

 account before we can determine [it]. Perhaps the mode of inves- 

 tigating this matter is not to depend upon active principles, or the 

 principle of life ; but to consider the matter of both [vegetables and 

 animals] when they are dying and when dead. In the first they may 

 show a peculiarity, and in the second they can both be considered 

 only as matter. 



Chemistry was, perhaps, the first mode of investigation: but that 

 science only considered them in two lights, viz. spontaneous changes, 

 and those produced by fire ; and, perhaps, the common modes of ana- 

 lysation by chemical processes have already gone as far as it was pos- 

 sible on this subject : nor was even chemistry employed to observe the 

 similarity between the two substances, but to find out the products of 

 each ; which, of course, gives us the similarity and dissimilarity of the 

 products. But, to prove the one or the other, a thousand experiments 

 might be made which would tend to throw some light upon this subject. 



I shall first consider what happens to both in the act of dying. 

 When an animal dies it soon becomes stiff; this arises from the mus- 

 cular fibres contracting in this act and not relaxing again ; besides 

 which, all the juices coagulate, which increases the rigidity. It con- 

 tinues in this state till putrefaction begins to dissolve the whole. 



When a vegetable dies it becomes immediately flaccid, and loses that 

 brittleness or crispness which a living vegetable has*. However, this 

 can only happen to those whose texture will admit of it, for the woody 

 part of a vegetable is so firm in its texture as to be little affected by 

 death : it is like a bone in an animal. Most of the circulating juices of 

 an animal coagulate, each by its different process : some by standing 

 either in or out of the circulation ; others by heat, alcohol, acids, &c. ; 

 excepting the red blood, which admits of being mixed with alcoholf. 



The juices of plants in general do not coagulate by any process yet 

 known J. They readily dissolve or mix with alcohol, by which means 



* Many substances kill vegetables sooner than others : vinegar is one. Therefore, 

 those who know how to make a salad will never mix the vinegar till the salad is just 

 going to be eaten. This effect might be supposed to be like an animal being killed 

 by electricity or lightning ; but I can only say that we have not an instance of a 

 vegetable becoming rigid by death in any way. 



t It is to be understood I speak of very fresh animal juices, for if they become 

 putrid they will dissolve in it. 



* Caoutchouc (India-rubber) may be supposed to be an exception to this. 



