Hot was the earth, and restless too, with booming, blowing volcanoes and tremulously trenching earthquakes. The conditions were not conducive to sustain any form of life. The mixture of escaping gases contributed to the formation of atmosphere around the earth. As the hot gases rose higher & higher, they cooled & condensed to form clouds. The hovering clouds gathered the electrical charges on their surfaces. The piling opposite electrical charges attracted each other causing lightening. With thunder -storms & cloud-bursts the torrential down pour cooled the earth and formed the oceans. The striking thunder-bolt in the medley of carbon, oxygen, hydrogen and nitrogen catalysed to synthesize a new organic molecule, the protoplasm. Thus life began on earth ! This conjecture of the scientists was later proved in a laboratory experiment by Stanley Millar and Dr.Khare. In a corked round-bottomed flask containing a mixture of carbon,oxygen,hydrogen and nitrogen,they sparked on electric flash of high voltage. Result:The specks of protoplasm were synthesized!. Life was born at the hands of the sons of man!! The protoplasm was unstable. It needed protection. The condensation of the protoplasm on the periphery provided the needed protection in the form of cell-membrane and the condensation in the center furnished the governing body, the nucleus. Thus an omnipotent, unicellular organism came into being. The scientists could not furnish the protoplasm these much needed facilities. Hence they are unsuccessful to synthesise an omnipotent cell in the laboratory. The ocean from without nurtured these unicellular organisms. They excreted their waste products in the ocean. This transfer occurred across the cell-membrane. As they evolved in the multicellular forms, the deeper cells were deprived of nutrition and could not excrete their waste. To overcome this difficulty, multiple intercommunicating channels developed. Thus the primitive lymphatic system was developed. As these multicellular animals evolved still further & formed an external protective covering, the open-channel lymphatic system became a closed lymphatic system.

At the periphery i.e. in the tissue-spaces the lymphatic vessels begin as microscopic closed-end or blind-end vessels, the lymphatic capillaries. They are formed by single layer of endothelial cells supported by the fibrous connective tissue. The capillaries join to form bigger lymphatic vessels. They gradually become bigger and bigger & enter the relay stations, the lymph nodes. The lymph circulates in the lymph nodes. From here the second set of lymph vessels come out, to be relayed to the second set of lymph nodes. All the lymph from the body is ultimately collected into two big channels-the right lymphatic duct & the left lymphatic duct (the thoracic duct). They open in the right and left subclavian veins respectively. The thoracic duct emerges from the receptaculum-Cisterna chyli. The cisterna chyli is situated in the abdomen, in front of the second lumbar vertebra. It receives lymph from both the lower limbs and from the alimentary canal. Each lymph node is a bean-shaped body. It is lovered by a thin capsule. From the capsule, the fibrous strands extend into the lymph-node & divides the node into many compartment. The lymph-node is divided into two zones, the outer cortex & the inner, medulla. Each lymph node is a collection of lymphoid tissue. The site on the surface of the lymph node at which the lymph vessels enter and leave is marked by a dimple; known as the hilum. The lymphatics entering the node are known as afferent-vessels and those leaving the node are known as the efferent-vessels.

The lymph contains 1) Water 94% 2) Solids 6%

The lymph is rich in its protein content. The protein content varies according to the region of the body from which the lymph is collected. The lymph from the liver is richest in its protein content,that from the intestines intermediate & that from the limbs poorest. In the state of fasting the fat content of the lymph is very low. After a fatty meal however the fat content may be very high. On the average,the sugar content of the lymph is about 120 mg.per 100ml. The other constituents of the lymph expressed in mgms per 100 ml are: Urea 23.5 Non-protein nitrogenous substances 34.8 Creatimine 1.4 Chlorides 714 Phosphorus 11.8 Calcium 9.84 The lymph is rich in various enzymes and antibodies When viewed under microscope it contains a large number of white blood cells(W.B.C.S .), Mostly the lympho cycles ranging from 500 to 75,000 per cu.mm.