182 EELATIONS OF BACTEEIA TO DISEASE 



in the blood — a neutrophile leucocytosis. And further, observa- 

 tion has shown that associated with this there is in , the 

 bone-marrow an increased number of the mother-cells of these 

 leucocytes — the neutrophile myelocytes. The passage of the 

 neutrophile leucocytes from the marrow into the blood, with the 

 resulting leucocytosis, is also apparently due to the absorbed 

 bacterial toxins acting chemiotactically on the marrow. These 

 facts abundantly show that the means of defence is not a mere 

 local mechanism, but that increased proliferative activity in 

 distant tissues is called into play. In addition to direct phago- 

 cytosis by these leucocytes, there is now abundant evidence that 

 an important function is the production in the body of bactericidal 

 and other antagonistic substances. In other cases the cells 

 chiefly involved are the mononuclear hyaline leucocytes, and 

 with them the endothelial cells, e.g., of serous membranes, often 

 play an important part in the defence ; this is well seen in 

 typhoid fever, where the specific bacillus appears to have little 

 or no action on the neutrophile leucocytes. In other cases, 

 again, the reaction is; chiefly on the part of the connective 

 cells, though their proliferation is always associated with some 

 variety of leucocytic infiltration and usually also with the forma- 

 tion of new blood vessels. Such a connective tissue reaction 

 occurs especially in slow infections or in the later stages of an 

 acute infection. The reactive tissue changes in the presence 

 of bacterial invasion are naturally very varied, — examples of 

 this will be found in subsequent chapters,— but they may be 

 said to be manifestations of the two fundamental processes of 

 (a) increased functional activity — movement, phagocytosis, secre- 

 tion, etc. — and (b) increased formative activity — cell growth 

 and. division. The exudation from the blood vessels has been 

 variously interpreted. There is no doubt that the exudate may 

 have bactericidal or opsonic properties and also acts as a 

 diluting agent, but it must still be held as uncertain whether 

 the process of exudation ought to be regarded as primarily 

 defensive or as the direct result of damage to the endothelium of 

 the vessels. It may also be pointed out that the various changes 

 referred to are none of them peculiar to bacterial invasion ; they 

 are examples of the general laws of tissue change under abnormal 

 conditions, and they can all be reproduced by chemical substances 

 in solution or in a particulate state. What constitutes their 

 special feature is their progressive or spreading nature, due to 

 the bacterial multiplication. 



(1) Local Lesions. — In some diseases the lesion has a special 

 site; for example, the lesion of typhoid fever, and, to a less 



