THE ANIMAL AS A PRIME MOVER. 327 



duced, and three times its actual efficiency under the most favorable 

 conditions yet reported. To attain this efficiency of the vital machine, 

 any heat engine acting under the laws of thermodynamics, as applied 

 to motors with fluid working substances, the only forms as yet devised, 

 must, if we take the temperature of the human body as its minimum, 

 have a range of about 375° F., and a maximum temperature of about 

 475° F. These should be the limiting temperatures of the machine, if 

 it were a thermodynamic engine operating under any such conditions 

 as are now known to limit the action of the heat engines. 



The maximum possible range of temperature in a mass of organic 

 substance of which 50 per cent or more is water, and the circulating 

 fluid mainly a solution of organic substance, can not possibly be much 

 greater than the range between the freezing and boiling points of 

 pure water, but the efficiency of the best heat engine known, even 

 acting as a perfect thermodynamic engine, would not exceed the ratio 

 180/672 = 0.27 (27 per cent) and its actual efficiency would probably 

 fall below 20 per cent. The animal — the vital engine — certainly has no 

 sensible range of working temperature, and no elastic working sub- 

 stance like the gases and vapors, but its efficiency, even as a work 

 producer alone, exceeds the above figure, and as an energy-producer 

 its efficiency exceeds that of ordinary heat engines several times. 



The correct method of estimating the efficiency of the vital machine 

 is unquestionably that which sums up all its expenditures of energy, 

 thermal, mechanical, mental, and determines the ratio of that sum of 

 all energies, so far as directly contributing to the purposes for which 

 the dweller within the apparatus lives, with the total energy supplied 

 during a period including at least one perfect cycle. Taken in this 

 manner and in this sense, the rejected heat would seem to constitute 

 the only real waste, and the efficiency of the machine, as a peripatetic 

 residence for the soul, would seem to be fairly reckoned at not less than 

 45 per cent nor more than 65, accordingly as one or the other of the 

 units above taken are accepted — two to three times the maximum 

 efficiency of the best-known heat engines. 



The rejected heat energy is precisely like that of the final heat waste 

 of the electric-lighting system — the final form of energy subjected to 

 transformations of greater or less complexity during the process of 

 application, in some definitely demanded phrase, to a prescribed pur- 

 pose. Eejected heat is certainly not, in the case of the vital machine, 

 "let down" from a higher temperature in the process of thermodynamic 

 conversion, an essential characteristic of that form of prime mover. 

 The machine is evidently not a thermodynamic engine. 



PART III.— SPECIAL ENERGY PRODUCTS: ELECTRICITY, LIGHT, ETC.; 

 SUMMARY AND CONCLUSIONS. 



Singular and unfamiliar energies are produced by the vital machine, 

 either as incidental to the ultimate purposes of the apparatus, or as 

 special final output for peculiar purposes. For example, it is known 



