 Six forms of external "tapas" are—fasting, control of appetite, accepting food under certain conditions, renunciation of delicious food, sitting and sleeping in lonely place and renunciation of comforts.Six forms of internal "tapas" are—atonement, reverence, rendering of service to worthy ones, spiritual study, avoiding selfish feelings and meditation.Justice Tukol notes that the supreme importance of the doctrine of karma lies in providing a rational and satisfying explanation to the apparent unexplainable phenomenon of birth and death, of happiness and misery, of inequalities and of existence of different species of living beings.