THE BLOOD AND THE BLOOD-FORMING ORGANS. 379 



dition is seen in some forms of anaemia. When the polynuclear neutro- 

 phile leucocytes alone are increased the condition is termed polynuclear 

 leucocytosis, or simply leucocytosis. If the inonoimclear cells are chiefly 

 affected, the condition may be denoted as lymphocytosis. The eosiuophile 

 cells alone may be increased. 



Polynuclear Leucocytosis may be either physiological or pathological. 



Physiological Polynuclear Leucocytosis is seen during normal digestion, 

 in the later months of pregnancy, in the first days of infancy, and is 

 usually of moderate grade. 



Pathological Polynuclear Leucocytosis occurs in many inflammatory and 

 infectious diseases, and accompanies the various cachexias. Of the in- 

 fed ions diseases attended with .leucocytosis may be mentioned pneu- 

 monia, diphtheria, scarlet fever, erysipelas, rheumatism, suppurative 

 cerebro-spinal meningitis, and any disease associated with a pronounced 

 exudative or suppurative, lesion. On the other hand, leucocytosis is 

 absent in uncomplicated typhoid fever, typhus, malaria, measles, and 

 tuberculosis. 



The origin and significance of the leucocytosis of infectious diseases 

 is imperfectly understood, but may be partially explained by the princi- 

 ples of chemotaxis and phagocytosis. From experimental evidence and 

 clinical observation it is known that during the onset of some infectious 

 diseases the entrance of bacteria or their products into the blood is fol- 

 lowed by a disappearance from the circulation of many polynuclear leu- 

 cocytes, which are removed from the larger vessels and lodged in the 

 capillaries, principally in the lungs and liver. This condition of the 

 blood, called hypoleucocyjtosis, may be attended with a transient reduction 

 Tnjffmpft^turejtnd weakening of the heart's action, and is usually suc- 

 ceeded shortly by the reappearance of polynuclear leucocytes in large 

 numbers, and by a ri>e of temperature. These leucocytes are apt to 

 gather in regions in which micro-organisms are abundant, and are be- 

 lieved to take up and destroy micro-organisms (phagocytosis), and to 

 prevent their further entrance, and possibly the entrance of their prod- 

 ucts also into the circulation. Of the place and method of origin of 

 these new leucocytes very little is definitely known. 



fflMTfl flf fofe|niia dfapasp such as pneumonia, 



diphtheria, and peritonitis, the initial hypoleucocytosis persists, in which 

 event the disease usually runs an asthenic and fatal course, with a ten- 

 dency to low temperature and feeble pulse. 



When leucocytosis is established the grade varies frequently with the 

 extent of the local lesion and the height of the fever associated with 

 the infectious process, and disappears with, or soon after, the decline of the 

 disease. In general, accordingJxMmr presen^knowledge, the leucocy- 

 tosis of infections diseases maybe regarded as the effort of the blood- 

 producing organs to protect the blood and tissues by means of leucocytes 

 against the invasion of micro-organisms and against the action of toxins 

 present in the circulation. 



The blood in typhoid fever presents a peculiar variation from that in 



