TUBERCULOSIS. l6l 



in the arterial blood. These in turn flow into the veins which 

 unite to form the oreat vein, or vena cava, which empties 

 into the right side of the heart. F'rom here it is pumped to 

 to the lungs to be purified and aerated again, coming into the 

 minute capillary network of the lungs, where the interchange 

 of gases takes place. From here it is taken up by the pul- 

 monary veins and carried to the left side of the heart, to be 

 pumped again to the different parts of the body. 



But along with and more minutely constructed than the 

 vessels carrying the circulation of the blood, is another circu- 

 latory system which is highly important to understand, called 

 the lymphatic system. This system, while it nourishes the 

 body by taking up or absorbing nutriment from the alimentary 

 tract and pouring it into the blood, and also directly nourishes 

 the body and certain non-vascular tissues, such as the cornea, 

 cartilage, etc., seems to have for its principal function that of 

 a drainage or sewerage system for the body. The tissues are 

 bathed in lymph which is contained in the lymphatic spaces 

 existing between the capillary blood vessels and capillary 

 lymph vessels. There is a constant passage of material from 

 the blood into the tissues, and from the tissues through the 

 capillaiy lymphatics into the main lymphatics, and from there 

 to the lymphatic duct and then into the venous system. Along 

 this lymphatic or sewage system, just before each vessel leaves 

 an organ of the l)ody, are situated little receptacles, or catch 

 basins, called lymph glands. Into these lymph glands are 

 poured the contents of the surrounding organ or parts. Here 

 the fluid is strained and worked over. If the tissues that 

 drain into this gland have been injured or have within them 

 any poisonous or effete material, it is deposited in this gland, 

 causing it to enlarge, become inflamed, or broken down, 

 according to the degree of injury or infection surrounding the 

 part. Thus it is that these little glands are the barometers or 

 danger signals of the body, and it is these and their condition 

 that we consult most freely in looking for bacteriological dis- 

 eases, particularly in the earlier stages of infection. 



