34 THE ANIMAL AS MACHINE 



Suppose we take a low figure for animal efficiency, say 20 per 

 cent. Then, substituting, we find that 



O1 "I OT "I 



Tj= =389 absolute or 116 C. 



X 02 U*o 



That is to say, in order to have an efficiency of 20 per cent, with 

 a condenser temperature of 38, the temperature of the heat 

 source would need to be 116 C. Experience teaches that the 

 production of any such temperature in any tissue would cause 

 death. Lethal temperature is somewhere about 47 C. How- 

 ever the animal may transform bound energy into free, it does 

 not do so by conversion to heat as one of the stages. 



It is not definitely known how the living organism is able to 

 make use of the chemical energy of the foodstuffs. Analogy 

 with familiar non-living machines breaks down here. An electric 

 battery is able to transform chemical energy into kinetic energy 

 without the middleman heat, the go-between in this case being 

 certain unknown but ordered atomic movements. Observation 

 shows clearly that muscle at least is not similar to an electric 

 motor. Similarly, one can dispose of all other forms of energy- 

 transformation used in machines to get work from bound energy. 



To attempt to gain an insight into the workings of the living 

 organism one must go back to elementary principles, and study 

 the machine itself. The history of the foodstuffs after ingestion 

 must be followed, and any changes they undergo must be noted. 

 The processes of digestion, absorption and assimilation will be 

 noted later. Meanwhile, we want to know what, in general, 

 happens to all foods used as sources of energy. Have they, in 

 the main, a common history ? Of one point at least we may be 

 sure, and that has been dealt with at some length in the preceding 

 chapter, namely, that liberation of energy in the animal and oxida- 

 tion are invariably concomitants. Thus the amount of oxidation 

 may be taken as a measure of the energy transformation. 



Again, it has been definitely proved that all energy changes 

 and all vital oxidations take place in the living cell. Physiological 

 chemists, while unable to arrive at a definite conclusion as to the 

 composition of the cell, are at one with the histologists in stating 

 that the cell material is of the nature of a solution. Cell proto- 

 plasm consists of over 75 per cent, of water acting as the solvent 

 for certain crystalloids and as the dispersion medium for various 

 colloids. The cell comes into intimate contact with other cells, 

 and all cell contents are not of the same chemical composition 



