CHAP. VIII Vitality 131 



a necessary part of the living matter, and that the nucleus 

 did not always occur. The cell is a machine, not in virtue 

 of the disposition of its visible parts, but as a consequence 

 of the arrangement of its molecules. We know this much 

 about the living machinery, that it is far more perfect 

 than the machinery of our steam-engines, the perfection of a 

 machine being measured by the relation between the energy 

 which enters it and that which leaves it as work done. 



" Joule pointed out that not only does an animal much 

 more nearly resemble in its functions an electro-magnetic 

 engine than it resembles a steam-engine, but also that it is 

 a much more efficient engine ; that is to say, an animal, 

 for the same amount of potential energy of food or fuel 

 supplied to it — call it fuel to compare it with other engines 

 — gives you a larger amount converted into work than any 

 engine which we can construct physically." And Joly has 

 expressed the contrast between an inanimate material 

 system and an organism as follows : " While the transfer 

 of energy into any inanimate material system is attended 

 by effects retardative to the transfer and conducive to dis- 

 sipation, the transfer of energy into any animate material 

 system is attended by effects conducive to the transfer 

 and retardative of dissipation." 



It is from protoplasm that we must start in our study 

 of living machinery ; let us see how far we can attain to 

 exact conceptions of its nature. We will first describe 

 shortly what is known as to the structure of protoplasm 01 

 living matter, chiefly to show how hopeless is any attempt 

 at a solution of the problem in terms of visible structure. 

 The powers of the microscope are limited by the physical 

 nature of light, and that limit has already nearly been 

 reached ; and yet we know the structure of matter is so ex- 

 cessively minute that within the compass of the finest fibre 

 visible with the microscope there is room for the most intri- 

 cate structural arrangements. 



6. Protoplasm. — Protoplasm used commonly to be de- 

 scribed as a structureless mass ; we now know that it often 

 has a structure somewhat like a heap of network. It is a 

 complex of finely-arranged strands, with knots or swellings 



