70 



GENERAL VIEW OF THE FUNCTIONS. 



composition, which can be made evident. In the ordinary death of an Ani- 

 mal, we may commonly trace the action of the morbific cause upon some par- 

 ticular organ, whose function is thereby either suspended or perverted ; and 

 the cessation of the whole train of actions necessarily results, if this organ be 

 one of those essentially concerned in them. Thus, to take a not uncommon 

 case, a patient with tubercular deposition nearly filling both lungs, becomes 

 the subject of an ulceration, which suddenly opens a passage from one of the 

 bronchi to the pleural cavity on the same side ; death from this cause is fre- 

 quently almost instantaneous, from the total incapacity of the other lung to 

 maintain by itself those respiratory actions which are necessary to the con- 

 tinuance of the circulation. Take again, for example, the influence of a nar- 

 cotic poison ; it occasions torpidity, first of the brain, and then of the medulla 

 oblongata. So long as its action is confined to the brain, the general train of 

 vital operations is no more disturbed than it is in profound sleep ; but as soon 

 as it affects the medulla oblongata, the respiratory movements become para- 

 lyzed (from causes hereafter to be explained), and the circulation is soon 

 brought to a stand ; and every organ in the body speedily loses its character- 

 istic properties, by the commencement of chemical changes in its composition. 

 But if the respiration be artificially sustained, the circulation will continue, 

 and all the processes of nutrition, secretion, &c., to Avhich it is subservient, 

 will be performed with little interruption. Hence the cessation of the whole 

 train, which would otherwise ensue, and the loss of vitality of the general 

 structure, are due to the local change produced by the morbific cause ; and 

 the same may be traced, though not always so evidently, in a variety of other 

 instances. 



74. If we consider the actions exhibited by any living being, in which they 

 are sufficiently complex and numerous to admit of being classified, we shall 

 perceive that they may be associated into groups, termed Functions; of which 

 every one, taken as a whole, has some positive and determinate purpose. 

 Thus, one of the most universal of all the changes necessary to the existence 

 of a living being, is the exposure of its nutritious fluid to the air ; by the 

 action of which upon it, certain alterations are effected. For the performance 

 of this aeration, simple as the change appears, many provisions are required. 

 In the first place, there must be an aerating surface, consisting of a thin mem- 

 brane, permeable to gases ; on the one side of which the blood may be spread 

 out, whilst the air is in contact with the other. Then there must be a provi- 

 sion for continually renewing the blood, which is brought to this surface ; in 

 order that the whole mass of fluid may be equally benefited by the process. 

 And, in like manner, the stratum of air must also be renewed, as frequently as 

 its constituents have undergone any essential change. We include, therefore, 

 in speaking of the Function of Respiration, not only the actual aerating pro- 

 cess, but also the various changes which are necessary to carry this into effect, 

 and which obviously have it for their ultimate purpose. 



75. On further examining and comparing these Functions, we find that they 

 are themselves capable of some degree of classification. Indeed, the distinc- 

 tion between the groups into which they may be arranged, is one of essential 

 importance in Animal Physiology. If we contemplate the history of the Life 

 of a Plant, we perceive that it grows from a germ to a fabric of sometimes 

 gigantic size, generates a large quantity of organized structure, and many 

 organic compounds, which form the products of secretion, but do not undergo 

 organization, multiplies its species, by the production of germs similar to that 

 from which it originated; but that it performs all these complex operations, 

 without (so far as we can perceive) either feeling or thinking, without con- 

 sciousness or will. All the functions of which its Life is composed, are, there- 

 fore, grouped together, under the general designation of Functions of Organic 



