26 INFECTION AND RESISTANCE 



organs directly from the initial focus by embolism or by the massive 

 invasion of a blood vessel. It is by such breaking into a vein that 

 Weigert explains the generalization of miliary tuberculosis. 



The inflammatory reaction which usually ensues at the point of 

 entrance of bacteria is merely a result of the local struggle between 

 invader and tissues, and the violence of this reaction is in a large 

 measure an indication of the resistance of the infected subject. 

 When, for instance, a streptococcus of moderate virulence gains 

 lodgment in the skin of a healthy individual the rapid mobilization 

 of leukocytic and other defences may prevent further invasion by 

 the bacteria and lead to a struggle which is clinically evidenced by 

 severe local symptoms. Did the virulence of the streptococci far 

 overbalance the powers of resistance the local struggle might be 

 reduced to a minimum, the infection progressing without any, or 

 with but a slight local, reaction. The fact that pneumococci lodging 

 in the human lung ordinarily cause lobar pneumonia is merely an 

 evidence of a considerable degree of resistance to these germs on the 

 part of the average human being. Pneumococci introduced into the 

 pulmonary alveoli of very susceptible animals (rabbits) may pass 

 directly through into the circulation, causing fatal septicemia with- 

 out leading to a more than mild and temporary reaction in the lungs 

 themselves. If, as in Wadsworth's 45 experiments, the rabbits are 

 partially immunized that is, their resistance increased before the 

 pulmonary inoculation is carried out a violent local reaction, anal- 

 ogous to lobar pneumonia, may follow, the severity of the reaction 

 at the portal of entry being manifestly an evidence of more energetic 

 opposition to further penetration of the bacteria. 



The entrance of bacteria into the deeper tissues, and even the 

 circulation, without any, or with but slight, local evidences of infec- 

 tion at the point of entrance is by no means rare. The innocent 

 appearance of the site of the entrance of the bacteria in generalized 

 streptococcus infection is a common surgical observation, and a strep- 

 coccus-infected wound of the hand or leg in a patient dying of septi- 

 cemia may appear but slightly inflamed and edematous and incom- 

 parably milder in appearance than a staphylococcus boil with which 

 the patient is walking about and suffering hardly any systemic dis- 

 turbance. 



Between the time of entrance of the bacteria into the body and 

 the first appearance of symptoms of disease there is always a definite 

 interval which is spoken of as "incubation time." This period is 

 made up of two definite divisions one the time necessary for 

 growth, distribution, and accumulation of the bacteria, the other the 

 time necessary for the action of the toxin or poison which may be 

 secreted. The latter, the incubation time of the toxin, is a subject 

 which is still unclear in many of its phases, and will be discussed 

 45 Wadsworth. Am. Jour, of the Med. Sc., Vol. 27, 1904. 



