222 SYMBWGENESIS 



Whether the distinction made by Liebeg (Spencer goes on to say) 

 between nitrogenous substances, as tissue-food, and non-nitrogenous 

 substances, as heat-food, be true or not in a narrower sense, it cannot 

 be accepted in the sense that tissue-food is not also heat-food. Indeed he 

 does not himself assert it in this sense. The ability of carnivorous 

 animals to live and generate heat while consuming matter that is almost 

 exclusively nitrogenous, to say nothing of the constant relation above 

 shown between functional activity and the evolution of heat, suffices to 

 prove that the nitrogenous compounds forming the tissues are heat- 

 producers, as well as the non-nitrogenous compounds circulating among 

 and through the tissues. But it is possible that this antithesis is not 

 true even in the more restricted sense. It seems quite an admissible 

 hypothesis that the hydro-carbons and oxy -hydro-carbons which, in 

 traversing the system, are transformed by communicated chemical action, 

 evolve during their transformation, not heat alone, but also other kinds 

 of force. It may be that as the nitrogenous matter, while falling into 

 more stable molecular arrangements, generates both that molecular 

 agitation called heat, and such other molecular movements as are 

 resolved into forces expended by the organism ; so, too, does the non- 

 nitrogenous matter. Or perhaps the concomitants of this metamor- 

 phosis of non-nitrogenous matter vary with the conditions. Heat alone 

 may result when it is transformed while in the circulating fluids, but 

 partly heat, and partly another force, when it is transformed in some 

 active tissue that has absorbed it : just as coal, though producing little 

 else but heat as ordinarily burnt, has its heat partially transformed 

 into mechanical motion if burnt in a steam-furnace. In such case, the 

 antithesis of Liebig would be reduced to this : that whereas nitrogenous 

 substance is tissue-food both as material for building up tissue and as 

 material for its function, non-nitrogenous substance is tissue-food only 

 as material for function. 



The example of the carnivora, as we have seen, fails to 

 provide the criterion of what constitutes wholesome nutrition. 

 That they cannot obtain the right kind of stimulation from 

 their food is, symbiogenetically speaking, certain. 



Spencer omits to note that carnivora rely retrogressive! y 

 upon those ancestral dynamics (symbiotics) which were at one 

 time characteristic of the whole mammalian order, and there- 

 fore are of considerable persistence, although in some instances 

 in course of dissipation. The capacity of chemical heat- 

 production once evolved, like so many other mammalian 

 traits and qualities, is not lost in a hurry, and the getting of 



