142 OF THE STRUCTURAL ELEMENTS OF THE HUMAN BODY. 



operative under some form ; and that in every case in which force seems to be 

 annihilated, it merely changes its modus operandi. Thus, when Motion is 

 retarded by friction, Heat is generated, with Electricity in addition whenever 

 the rubbing surfaces are otherwise than perfectly homogeneous ; so when Heat 

 is caused to vaporize water, it no longer manifests itself as Heat, but in the 

 form of mechanical power which produces Motion ; and the discharge which 

 restores the Electric equilibrium is in like manner attended with the develop- 

 ment of Mechanical force. 1 It will be found that, in all instances in which such 

 a conversion or metamorphosis of force takes place, some material substratum is 

 required as its instrument. This may be, in some cases, of almost any descrip- 

 tion whatever ; as when Heat is produced by the friction (or retarded motion) 

 of solids, liquids, or even gases ; or when Motion (as shown in expansion) is 

 produced by the application of heat to any kind of material substance. But in 

 other cases, the change can only be effected through some special kind of instru- 

 ment ; or, if several substances may serve as its medium, there is some one 

 which is greatly superior to every other, in the readiness with which a certain 

 force manifests itself through it. Thus, iron is the substance through which an 

 Electric current can best develop Magnetic force ; a combination of bismuth and 

 antimony is that through which Heat can best generate Electricity ; and the 

 affection of Light by Magnetism, though producible through any transparent 

 medium (but not through a vacuum), can be made much more obvious when 

 the magnetism is made to act upon a glass composed of vitrified borate of lead, 

 than through the medium of any other substance yet known. It is, indeed, on 

 this speciality in the action of different substances, when subjected to the influ- 



1 [The doctrine of the correlation of the Physical forces here alluded to has never as 

 yet, we believe, been accredited to its true source. The treatise of Prof. Grove on the 

 Correlation of the Physical Forces is usually regarded as the first publication on this sub- 

 ject. It is dated 1843. This was followed by that of Dr. J. R. Mayer, dated Heilbronn, 

 1845. Subsequently there have appeared the author's memoir on the " Mutual Relations 

 of the Physical and Vital Forces," in 1850; and Mr. Newport's paper "On the Reciprocal 

 Relation of the Vital and Physical Forces," 1850. In anticipation of all these, however, 

 the doctrine was formally enunciated from the chair of "Institutes of Medicine" by Prof. 

 Jackson of the University of Pennsylvania, as early as the year 1837, as will be seen by 

 the following extract from an introductory lecture delivered and published at that time. 

 "Physical phenomena, according to the class they belong to, are referred to a few simple 

 laws, as gravity, caloric, affinity, galvanism, electricity, magnetism ; all of which, it can 

 now be scarcely doubted, are modifications of one great force. The force producing phy- 

 siological or organic phenomena may be no more than a modification of the same ruling 

 power displaying its activity in organized matter. Movements, the influence or powers 

 that cause them, the directions they assume from the combined influence of powers and 

 resistances, intrinsic or external, when studied in inorganic bodies, constitute physics; 

 and in organized bodies, physiology, or, as it may be more aptly named, organic physics" ' 



The explanation of many of the phenomena of living beings, hitherto regarded as vital 

 phenomena, upon chemical and physical principles, has been taught by Prof. Jackson for 

 the last eight years, and a large portion of his course has been devoted to the classification 

 and arrangement of them into the separate classes to which they belong ; thus, the pro- 

 duction of the immediate materials of organic tissue by a transformation of albumen, di- 

 gestion, calorification, and secretion, are classed as chemical actions ; absorption, endos- 

 mose, -muscular electricity, vision, hearing, voice, belong to physics. The spinal functions 

 are purely dynamic ; the muscular functions are mechanical. The principles of mechanics 

 are applicable to the explanation of the circulation a hydraulic apparatus ; to locomotion, 

 general or partial ; and to the operation of ingestion and egestion. 



In the second edition of Prof. Grove's treatise on the " Correlation of Forces," published 

 in 1850, the following remarks occur: "I believe that the same principle and mode of 

 reasoning as have been adopted in this essay, might be applied to the organic, as well as 

 to the inorganic world; and that muscular force, animal and vegetable heat, &c., might, 

 and at some time will, be shown to have similar definite correlation." The correlation 

 between the mechanical force of the muscular system and heat was announced in a paper 

 read by Prof. Jackson before 'the American Medical Association in 1849, and published in 

 their 'Transactions" for the year 1849. Ed.~\ 



