324 THE ANIMAL AS A PRIME MOVER. 



system also is thus rejected as heat, and assuming that the energy of 

 brain and nerve action is transformed into mental and un measurable 

 energies of which we have no dynamic equivalent yet established, the 

 animal machine, as represented by the human body, may be taken as 

 having an efficiency measured by the ratio of the sum of useful muscular 

 labor and brain work to the energy supplied. 



This is now seen to be probably not far from 30 per cent, and the 

 machine is, thns viewed, one and a half times as efficient as any exist- 

 ing steam engine. 



If the use of the machine may be taken to be the production of 

 muscle and brain work, and of the heat required for the comfort of the 

 system considered as an intelligent creature, the efficiency becomes 

 the sum of these three quantities, divided by the total receipts of 

 energy, or substantially two-thirds, the only waste on this basis being 

 that of unassimilated food, and the energy of formation of chemical 

 compounds, of heat, and of dynamic energy, unutilized, in a compara- 

 tively small proportion. 



Brain ivorli is the task and thought the product of the professional 

 man. The mass and weight of the brain give us some interesting data 

 for consideration, if not throwing important light upon the problem in 

 hand. The average weight of the brain of a man is about 3 pounds, 

 perhaps 50 ounces; that of the average woman is 10 per cent less, 

 about 45 ounces. High brain weights are 53.4 ounces, the weight of 

 that of Agassiz, up to 64.5, that of Cuvier; while low weights are 

 indicative of reduced working power, if not of capacity for intellectual 

 action. It is, however, true that the largest brains have been those 

 of the idiotic and the insane, and that the greatest genius sometimes 

 possesses a brain of but average size or even somewhat less; yet 

 insanity and idiocy only prove, in most cases, disease of the ordinary 

 brain of whatever size, and individual cases afford no evidence pro or 

 con. The important fact is that size of brain increases with the intel- 

 ligence of the race, and that when the weight falls below about 2 

 pounds, two-thirds the average for our own race, intelligence is usually 

 lacking. Cerebration only occurs, efficiently, with larger proportions 

 of gray matter. 



The average weight of the male brain in African races is about that 

 of females of the European races, and that of their females is 10 per 

 cent lower. The weights in Australian races fall to that of the African 

 female in the case of the male, and 10 per cent below this for the 

 female, or 39 ounces. The weight never exceeds 55 ounces, except 

 among the most civilized races. The bodily functions may be main- 

 tained and manual labor performed with very low weights, as healthy 

 idiots have been known having brains weighing less than a pound 

 (8.5 to 10.6 ounces). The cerebrum constitutes 87 per cent of the cra- 

 nial contents. 



The compactness and firmness of the brain substance and the com- 

 paratively small quantity of blood with which it is saturated in its 



