The food that you take consists of nitrogenous elements and proteins, fats or hydrocarbons such as ghee and carbohydrates such as rice and sugar. Proteins build up the tissues and the muscles. Carbohydrates produce energy. Besides these, there are various kinds of salts also. The various digestive juices, saliva in the mouth, gastric juice in the stomach, bile, pancreatic juice and the Succusentericus or the intestinal juice in the intestines act upon the particles of food during their passage in the alimentary canal or digestive tube.
Saliva acts upon starch. It converts it into sugar. This action is further taken by pancreatic and intestinal juice, in the intestines. Bile acts upon fats. Gastric juice and pancreatic juice act upon proteins. The whole thing is converted into a milky juice called chyle. This chyle is absorbed by lacteal vessels and it is mixed with blood.
The right side of the heart contains impure blood. This impure blood is sent to the lungs for purification and after being purified is brought back to the left side of the heart, and from there it is pumped through the big artery aorta, throughout the body. In the capillaries the blood exudes as lymph and bathes and nourishes the tissues and cells of the body, and the impure blood is carried back by veins to the right side of the heart.
The waste products of food are carried along the large intestine which is six feet in length to the rectum where it is retained as faecal matter. When the nervous impulse is carried to the rectum from the defaecation centre in the spinal cord, it is discharged through the anus, the terminal opening of the alimentary canal.
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