nostrils alone, but passes by the channel beside the uvula where the

extremity of the roof of the mouth is, some of the air going this

way through the apertures of the nostrils and some through the

mouth, both when it enters and when it passes out. Such then is the

nature and magnitude of the difficulties besetting the theories of

other writers concerning

respiration.

14



We have already stated that life and the presence of soul involve

a certain heat. Not even the digesting process to which is due the

nutrition of animals occurs apart from soul and warmth, for it is to

fire that in all cases elaboration is due. It is for this reason,

precisely, that the primary nutritive soul also must be located in

that part of the body and in that division of this region which is the

immediate vehicle of this principle. The region in question is

intermediate between that where food enters and that where excrement

is discharged. In bloodless animals it has no name, but in the

sanguineous class this organ is called the heart. The blood

constitutes the nutriment from which the organs of the animal are

directly formed. Likewise the bloodvessels must have the same

originating source, since the one exists for the other's behoof-as a

vessel or receptacle for it. In sanguineous animals the heart is the

starting-point of the veins; they do not traverse it, but are found to

stretch out from it, as dissections enable us to see.

Now the other psychical faculties cannot exist apart from the

power of nutrition (the reason has already been stated in the treatise

On the Soul), and this depends on the natural fire, by the union

with which Nature has set it aglow. But fire, as we have already

stated, is destroyed in two ways, either by extinction or by

exhaustion. It suffers extinction from its opposites. Hence it can

be extinguished by the surrounding cold both when in mass and