Observations placeholder

Avicenna (1999). The Canon of Medicine (al-Qānūn fī'l-ṭibb), vol. 1. Laleh Bakhtiar (ed.), Oskar Cameron Gruner (trans.), Mazhar H. Shah (trans.). Great Books of the Islamic World

……..when we reflect .. in regard to nutriment, our health depends on the nutriment being appropriate for us and regulated in quantity and quality. For not one of the aliments which are capable of nourishing the body is converted into actual nutriment in its entirety. In every case digestion leaves something untouched, and nature takes care to have that evacuated.

Nevertheless, the evacuation which nature accomplishes is not a complete one. Hence at the end of each digestion there is some superfluity left over. Should this be a frequent occurrence, repetition would lead to further aggregation until something measurable has accumulated. As a result, harmful effete substances would form and injure various parts of the body. When they undergo decomposition, putrefactive diseases arise [bacterial infections]. Should they be strong in quality, they will give rise to intemperament; and if they should increase in quantity, they would set up the symptoms of plethora which have already been described. Flowing to some member, they will result in an inflammatory mass, and their vapors will destroy the temperament of the substantial basis of the breath.

That is the reason why we must be careful to evacuate these substances. Their evacuation is usually not completely accomplished without the aid of medicines, for these break up the nature of the effate substances. This can be achieved only by 'toxic agents', although the drinking of them is to a certain extent deleterious to our nature. As Hippocrates says: "Medicine purges and ages." More than this the discharge of superfluous humor entails the loss of a large part of the natural humidities and of the breath, which is the substance of life. All this is at the expense of the strength of the principal and the auxiliary members, and therefore they are weakened thereby. These and other things account for the difficulties incident to plethora, whether they remain behind in the body or are evacuated by it.

Now exercise is that agent which most surely prevents the accumulation of these matters, and prevents plethora. The other forms of regiment assist it. It is this exercise which renews and revives the innate heat, and imparts the necessary lightness to the body, for it causes the subtle heat to be increased and daily disperses whatever effete substances have accumulated; the movements of the body help them to expel them conveying them to those parts of the body whence they can readily leave it. Hence the effete matters are not allowed to collect day after day and besides this, as we have just said, exercise causes the innate heat to flourish and keeps the joints and ligaments firm, so as to be always ready for service, and also free from injury. It renders the members able to receive nutriment, in being free from accumulated effate matters. Hence it renders the members light and the humidities attenuated, and it dilates the pores of the skin.

To forsake exercise would often incur the risk of "hectic", because the instinctive drives of the members are impaired, inasmuch as the deprivation of movement prevents the access to them of the innate breath. And this last is the real instrument of life for every one of the members.