It would seem to be Harvey's tendency to adhere to the view which limited the use of respiration entirely to the cooling and ventilation of the innate heat, by which according to ancient doctrine the heart was the central hearth, embedded in the cooling and ventilating lungs; although this ancient doctrine tallied well in most eyes with the belief that only a portion of the blood ever entered the heart at all.[80] In the first of the two Exercises which Harvey, when seventy years old, in 1649, addressed to Riolanus in defense of the circulation, the ancient respiratory cooling and ventilation take their place again as follows:-- "Thus by the aid of two extremes, viz.: cold and heat, is the temperature of the animal body retained at its mean. For as the air inspired tempers the too great heat of the blood in the lungs and centre of the body and effects the expulsion of suffocating fumes, so in its turn does the hot blood, thrown through the arteries into the entire body, cherish and nourish and keep alive all the extremities, preventing extinction due to the power of external cold."[81] In none of the writings of his old age does Harvey deal expressly with concoction in the lungs, or more than cursorily with the entrance of the substance of air into the blood. But he repeatedly and emphatically reaffirms that blood and spirits are one thing;[82] he even declares the blood in comparison with the other parts of the body to be "possessed of powers of action beyond all the rest, and therefore, in virtue of its preëminence, meriting the title of spirit."[83] He castigates those who give the rein to overmuch speculation about the spirits. We learn that some suppose that the spirits "are engendered and are fed and increased from the thinner part of the blood"; that others suppose "the primigenial moisture" to engender and support them.[84] Then there are "those who tell us that the spirits are formed in the heart, being compounded of the vapours or exhalations of the blood (excited either by the heat of the heart or the agitation) and the inspired air"[85]--the Galenic doctrine. "Such spirits," says Harvey of these last mentioned, "are rather to be regarded as fumes and excrementitious effluvia of the blood and body, like odours, than as natural artificers; ... whence it seems probable also that pulmonary expiration is for the ventilation and purifying of the blood by the breathing out of these; while inspiration is in order that the blood, in passing through between the two ventricles of the heart, may be tempered by the ambient cold; lest the blood, being hot and swollen, blown up in a sort of ferment, like milk and honey boiling up, should so distend the lungs that the animal would be suffocated."[86]