सन्तत्या भोज्यधातूनां परिवृत्तिस्तु चक्रवत् ।
(च. चि. १५/२१)
Formation of dhatu is a continuous process. Charaka has compared dhatu formation to fetching of water with pulley from well. Charaka further elaborates that dhatu formation depends on activity of dhatu-agni.
Due to hyperactivity of dhatu-agni, the process of dhatu formation becomes rapid. On other hand dhatu formation will slow down if there is hypoactivity of dhatu-agni.
According to Charaka Samhita in one week all seven dhatus are formed. Rasa dhatu is formed on first day after ingestion of food and shukra dhatu is formed on seventh day.
Sushruta has expressed different opinion about time factor regarding dhatu formation. According to Sushruta after formation of ahara rasa every dhatu is formed serially on every fifth day. Rasa dhatu is formed on first day of ingestion of food and on every fifth day, other new dhatu is formed. Hence shukra dhatu is formed on 30th day.
| Dhatu | Charak Samhita | Sushruta Samhita |
|---|---|---|
| Rasa | 1st day | 1st day |
| Rakta | 2nd day | 5th day |
| Mamsa | 3rd day | 10th day |
| Meda | 4th day | 15th day |
| Asthi | 5th day | 20th day |
| Majja | 6th day | 25th day |
| Shukra | 7th day | 30th day |
Time taken for dhatu formation is important to understand duration and effect of chikitsa (treatment) of particular dhatu. For Example – Effect of hematinic medicines on rakta dhatu can be observed only after five days from the onset of chikitsa because rakta dhatu is formed on fifth day. Twenty one days are required for healing of the fractured bone, as asthi dhatu is formed on twentieth day.