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outline, drawn by no master's hand : yet even such an outline may, I trust, 

 suffice for my main purpose. 



The branch of physics most closely connected with our subject is known 

 as Comparative Physiolgy. In this department of physical inquiry the 

 ultimate object is nothing less than to discover the plan of Organic Nature in 

 both the great kingdoms, the Animal and the Vegetable. Tbe special 

 instrument of inquiry is collation or comparison of one organic form with 

 another, with a view to ascertain the characteristic of each, and thence to infer 

 their relation to one another, and to the whole organic world. This science, 

 like every other part of physical investigation, assumes, of necessity, the 

 existence of a general plan or scheme of things ; a plan or scheme towards the 

 discovery of which the Human Intellect is capable of advancing. What then 

 has this science to say on the subject of our inquiry. 



In the comparison of organic forms the first great division which presents 

 itself is that already noticed, into Animal and Vegetable. So vast is the 

 difference between the more highly organised members of either kingdom — 

 take for instance a Lion and an Oak-tree — that the untrained mind at first 

 refuses to conceive of a possible relation between such diverse forms. Yet when 

 compared with inorganic matter, with clay or granite, it is seen at once that 

 beast and tree resemble each other in presenting, though under such different 

 aspects, the grand phenomenon of vitality ; and we express this very simple 

 fact when we say that they are both alive. Science has revealed in detail 

 many points of resemblance between Animal and Vegetable organisms. In 

 both, provision is made for nutrition, and for the reproduction of the species : 

 both also possess an apparatus for the circulation of the nutrient fluid, and for 

 respiration. And, broad as is the distinction manifest between the Animal 

 and Vegetable, when each is highly organized, it is matter of great difficulty 

 to discriminate between the lowest forms of the two kingdoms. Common 

 observation recognises this in the designation, "Animal-plant," popularly applied 

 to the sea anemone, and other creatures of the same class. The great vital 

 divisions may be likened to two stems of a tree which divide close to the 

 ground : as the topmost branches of each are those which have the least con- 

 nection, so does the highest vegetable seem farthest removed from the highest 

 animal organisation. On the other hand, the two kingdoms seem to coalesce 

 at their respective bases ; just as do the stems of the tree at the point where 

 they branch out. Now, amongst the grounds of distinction between Animals 

 and Plants, there is this possibly essential difference; at all events it is the 

 difference to which I shall specially direct jour attention to-night — Plants are 

 destitute of any nervous system.* The characteristic difference hence arising 

 between Animal and Vegetable life is thus expressed by Dr. Carpenter, " The 

 whole nisus (effort, striving) of Vegetative existence consists in the activity of 

 the organs of nutrition and re-production ; but, on the other hand, the nisus 

 of animal life tends towards the evolution of the faculties of sensation, and of 

 self-determined motion ; and in its highest manifestation to that of the intelli- 

 gence and will." So that there is, you see, a kind of life common to both 

 Animal and Vegetable, which the great French Anatomist, Bichat, has termed 

 " Organic Life;" sometimes also called "Vegetative Life,'" as being the only life 

 possessed by plants ; and there is another kind of life confined to animals, 

 termed by Bichat, 'Animal Life ;" and which I shall sometimes refer to as 

 "Nervous Life." In the animal, the stomach, intestines, and glandular 

 system, and, in some degree, the apparatus for circulation, are organs of the 



* The appearance of nervous irritability presented by parts of particular plants, as by 

 tbe leaflets of the sensitive plant, and the stamens of the barberry, is pronounced to be 

 due to a different cause. 



