مُحَمَّدُ بْنُ يَحْيَى عَنْ أَحْمَدَ بْنِ مُحَمَّدٍ عَنِ ابْنِ سِنَانٍ قَالَ سَمِعْتُ أَبَا الْحَسَنِ (عليه السلام) يَقُولُ طَبَائِعُ الْجِسْمِ عَلَى أَرْبَعَةٍ فَمِنْهَا الْهَوَاءُ الَّذِي لَا تَحْيَا النَّفْسُ إِلَّا بِهِ وَ بِنَسِيمِهِ وَ يُخْرِجُ مَا فِي الْجِسْمِ مِنْ دَاءٍ وَ عُفُونَةٍ وَ الْأَرْضُ الَّتِي قَدْ تُوَلِّدُ الْيُبْسَ وَ الْحَرَارَةَ وَ الطَّعَامُ وَ مِنْهُ يَتَوَلَّدُ الدَّمُ أَ لَا تَرَى أَنَّهُ يَصِيرُ إِلَى الْمَعِدَةِ فَتُغَذِّيهِ حَتَّى يَلِينَ ثُمَّ يَصْفُوَ فَتَأْخُذُ الطَّبِيعَةُ صَفْوَهُ دَماً ثُمَّ يَنْحَدِرُ الثُّفْلُ وَ الْمَاءُ وَ هُوَ يُوَلِّدُ الْبَلْغَمَ.
297. Muhammad Bin Yahya, from Ahmad Bin Muhammad, from Ibn Sinan who said: I heard Abu Al-Hassan  saying: ‘The body is built upon four, so from it is the air without which ‘the self’ cannot survive except by its (in and out) flow, and it takes out the diseases which are in the body and the decay, and the dirt (earth) which gives causes the dryness, and the energy (heat), and the food and from it the blood is generated. Indeed! Have you not seen that it (food) goes into the stomach, which digests it until it becomes soft, then cleans it? So the natural process takes the clean blood, then the residue descends along with the water, and it gives birth to the phlegm’.