THE VITAL AND PHYSICAL FORCES. 
737 
In order to meet the more varied requirements of the Animal organism, a much 
larger proportion of its tissues undergoes various transformations, so as to depart 
more or less widely from tlm original cellular type, than we find to he the case in the 
plant; still it is no less true in the animal than in the plant — as proved by the re- 
searches of Schwann, extended and confirmed as they have been in this particular 
by the researches of all subsequent histologists — that all the tissues possessing distinctly 
vital endowments^ , originate, directly or indirectly, in the transformation of cells. And 
further, it may be stated, that all the most active vital operations, in the Animal as 
in the Vegetable organism, are performed by tissues which retain their original cellu- 
lar constitution with little or no changef. 
The several modifications of vital force which have now been enumerated will be 
found, when closely examined, to have a very intimate mutual relationship, however 
dissimilar may be the phenomena they produce. In the first place they are all ex- 
erted, even in the most highly organized living being, through a common instrumen- 
tality, the simple cell. Secondly, the entire assemblage of cells making up the totality 
of any organism, have all a common parentage ; being linearly descended from the 
single primordial cell in which the organism originated. Thirdly, they are mani- 
fested in connection with each other, in those single-celled organisms, which are the 
lowest members of the two kingdoms respectively, and in which there is no sepa- 
ration or specialization of function. — Hence we may express them collectively under 
the general term of Cell-force ; and seem entitled to affirm that each is a particular 
modus operandi of the same force as that which is concerned in cell-formation 
* It may now be considered as a well-established fact, that the simple fibrous tissues may originate in a 
structureless blastema, and may be produced by its fibrillation, without passing through the intermediate con- 
dition of cells. But these tissues cannot be regarded as possessing any truly vital endowments ; their proper- 
ties being simply physical, and their uses in the economy merely mechanical. 
t This general proposition was first advanced by the author in regard to the operations in which organic life 
consists (and which are common, therefore, to plants and animals), in his “ Report on the Origin and Functions 
of Cells ” in the Brit, and For. Med. Review for January 1843. The subsequent discovery of the cellular 
composition of the ultimate fibrilla of striated muscular fibre, by himself and Prof. Sharpey contemporaneously, 
and the accumulation of various facts relative to the existence of cells or cell-nuclei at the peripheral extremi- 
ties of the afferent nerves, as well as in the central organs, seem to justify the assertion that unmetamorphosed 
cells are the active agents in the production of Muscular and Nervous force; in the former case effecting con- 
traction by their change of form, and in the latter developing nerve-force, which is transmitted along the fibres 
as its conductors. 
j; The author is particularly desirous that he should be understood as implying by the term “ cell-force,” 
not that the force is produced or generated by the cell, but that the growth of the cell is the most general 
objective manifestation of that force, and that the cell affords the ordinary instrumental condition for its exer- 
tion, though there can be no doubt that the force may be exerted in many cases in which cell-development 
does not take place. The use which he would make of the term is just that which is commonly made of the 
term “ Engine-power ; ” every one knowing that the steam-engine possesses no power itself, but that it is 
simply the instrument most commonly employed, because the most convenient and advantageous yet devised, 
for the application of the expansive force of steam, generated by the application of heat, to the production of 
mechanical motion. 
5 B 
MDCCCL. 
