I say, that the animal motions are not subject to our exterior senses; for I do not mean all exterior animal motions, nor all interior animal motions; for though you do see no interior motion in an animal body, yet you may feel some, as the motion of the Heart, the motion of the Pulse, the motion of the Lungs, and the like; but the most part of the interior animal motions are not subject to our exterior senses; nay, no man, he may be as observing as he will, can possibly know by his exterior senses all the several and various interior motions in his own body, nor all the exterior motions of his exterior parts: and thus it remains still, that neither the subtillest motions and parts of matter, nor the obscure passages in several Creatures, can be known but by several parts; for what one part is ignorant of, another part is knowing, and what one part is knowing, another part is ignorant thereof; so that unless all the Parts of Infinite Matter were joyned into one Creature, there can never be in one particular Creature a perfect knowledg of all things in Nature. Wherefore I shall never aspire to any such knowledg, but be content with that little particular knowledg, Nature has been pleased to give me, the chief of which is, that I know my self, and especially that I am, Madam, _Your constant Friend,_ _and faithful Servant._ [1] _Ch._ 61. called, _The Preface_. XLIV. _MADAM,_ I perceive you are desirous to know the cause, _Why a man is more weak at the latter end of a disease then at the beginning, and is a longer time recovering health, then loosing health_; as also _the reason of relapses and intermissions?_ First, as for weakness and strength, my opinion is, they are caused by the regular and irregular motions in several parts, each striving to over-power the other in their conflict; and when a man recovers from a disease, although the regular motions have conquered the irregular, and subdued them to their obedience, yet they are not so quite obedient as they ought, which causes weakness: Neither do the regular motions use so much force in Peace, as in War; for though animate matter cannot lose force, yet it doth not always use force; neither can the parts of Nature act beyond their natural power, but they do act within their natural power; neither do they commonly act to the utmost of their power. And as for Health, why it is sooner lost then recovered; I answer, That it is easier to make disorders then to rectifie them: as for example, in a Common-wealth, the ruines of War are not so suddenly repaired, as made. But concerning Relapses and Intermissions of diseases, Intermissions are like truces or cessations from War for a time; and Relapses are like new stirs or tumults of Rebellion; for Rebels are not so apt to settle in peace as to renew the war upon slight occasions; and if the regular motions of the body be stronger, they reduce them again unto obedience. But diseases are occasioned many several ways; for some are made by a home