GENERAL CONSIDERATIONS. 487 



effete matter, incapable of any further animal functions ; and what is it that gives to 

 these parts the power of self-regeneration, when new matter is presented under proper 

 conditions ? 



These questions are the physiological ignis fatuus, which, it is to be feared, will forever 

 elude the grasp of scientific inquiry. They constitute one of the great mysteries ever 

 present in the mind of the student of Nature, and one, the grandeur of which is so 

 immense that it is a problem with which our intelligence can scarcely grapple. Its 

 greatness is commensurate with that of the question of the soul, and its relations to the 

 finite and the infinite ; a question which philosophers have been constrained either to 

 admit upon the faith of revelation or to hopelessly abandon. Little if any real progress 

 is to be made by endeavoring to cover the inscrutable problem of life with a simplicity 

 entirely artificial. This will always be attractive, and, to a certain extent, satisfactory to 

 the minds of those unacquainted with the details of natural laws or willing to admit 

 speculative theories upon subjects concerning which it is impossible, in the present con- 

 dition of science, to have any positive information ; and, if generally admitted by biologi- 

 cal students, it would carry our science back to the dark periods in its history, when the 

 study of Nature was confined to speculation, and there existed no knowledge based upon 

 the direct observation of phenomena. A new name, arbitrarily applied to organic matter, 

 without any addition to its physiological history, does not advance our definite knowledge. 

 For example, it has long been known that certain nitrogenized constituents of the organ- 

 ism, classed collectively as organic principles, seem to give to the tissues their property 

 of self-regeneration and development. It may seem to those not engaged in scientific 

 inquiry that a recital of the wonderful properties of " protoplasm " affords some additional 

 information concerning the phenomena observed in organized bodies ; but the true defi- 

 nition of the term leads us back to our former ideas of the so-called vital properties of 

 organic matters. 



It is a well-established fact that, while nearly all of the tissues undergo disassimila- 

 tion, or conversion into effete matter, during their physiological decay in the living or- 

 ganism, others, like the epidermis and its appendages, are gradually desquamated, and, 

 when once formed, do not pass through any farther changes. The whole question of the 

 essence and nature of the nutritive property or force resolves itself into vitality. Life is 

 always attended with what we know as the phenomena of nutrition, and nutrition does 

 not exist except in living organisms. When we can state positively what is life, we shall 

 know something of nutrition. At present, physiologists have been able to define life 

 only by a recital of certain of its invariable and characteristic attendant conditions ; and 

 yet there are few, if any, definitions of life regarding' it as the sum of the phenomena 

 peculiar to living organisms that are not open to grave objections. 



If we regard life as a principle, it stands in the relation of a cause to the vital phe- 

 nomena ; if we regard it as the totality of these phenomena, it is an effect. 



If we study the development of a fecundated ovum, life seems to be a principle, giv- 

 ing the wonderful property of appropriating matter from without, until the germ 

 becomes changed, from a globule of microscopic size and an apparently simple structure, 

 into a complete organism with highly-elaborated parts. This organism has a definite 

 form and size, a definite period of existence, and it produces, at a certain time, generative 

 elements, capable of perpetuating its life in new beings. "We may say that an organism 

 dies physiologically because the vital principle, if we admit the existence of such a prin- 

 ciple, has a limited term of existence. But, on the other hand, the fully-developed living 

 organism, which we call an animal, presents numerous distinct parts, each endowed with 

 an independent property called vital, that property recognized by Haller in various tis- 

 sues, under the name of irritability ; and it is the coordinated sum of these vitalities that 

 constitutes the perfect being. These are more or less distinct ; and we do not commonly 

 observe a sudden and simultaneous arrest of the vital properties in all the tissues, m 

 what we call death. For example, the nerves may die before the muscles, or the mus- 



