162 RELATIONS OF BACTERIA TO DISEASE. 



occurs to so great a degree, the organisms rarely remain in large 

 numbers in the circulating blood, and their detection in it during 

 life by microscopic examination is rare, and even culture methods 

 may give negative results unless a large amount of blood is used, 

 yet it is interesting to note that the researches of Schottmiiller, 

 Auerbach and Unger, Cole and others, show that in various 

 septicaemias, pneumonia, and typhoid fever the blood may con- 

 tain at certain periods of the diseases the specific micro-organ- 

 isms in a relatively large percentage of cases. 



However, in fatal cases where blood cultures are negative 

 during life, the organisms may be found post mortem lying in 

 large numbers within the capillaries of various organs, e.g. in 

 cases of septicaemia produced by streptococci. (Relapsing fever 

 forms an exception, as in it numerous organisms may be seen in 

 a drop of blood.) In the human subject more frequently one 

 of two things happens. In the first place, the organisms may 

 remain local, producing little reaction around them, as in teta- 

 nus, or a well-marked lesion, as in diphtheria, pneumonia, etc. 

 Or, in the second place, they may pass by the lymph or blood 

 stream, to other parts or organs in which they settle, multiply, 

 and produce lesions, as in tubercle. 



2. Production of Chemical Poisons. In all these cases the 

 growth of the organisms is accompanied by the formation of 

 chemical products, which act generally or locally in varying 

 degree as toxic substances. The toxic substances become dif- 

 fused throughout the system, and their effects are manifested 

 chiefly by symptoms such as the occurrence of fever, disturb- 

 ances of the circulatory, respiratory, and nervous systems, etc. 

 In some cases corresponding changes in the tissues are found, 

 for example, the changes in the nervous system in diphtheria, to 

 be afterwards described. The general toxic effects may be so 

 slight as to be of no importance, as in the case of a local suppu- 

 ration, or they may be very intense, as in tetanus, or again, less 

 severe but producing cachexia by their long continuance, as in 

 tuberculosis. 



The occurrence of local tissue changes or lesions produced in 

 the neighbourhood of the bacteria, as already mentioned, is one 

 of the most striking results of bacterial action, but these also 

 must be traced to chemical substances formed in or around the 

 bacteria, and either directly or through the medium of ferments. 



