CHAPTER III 

 INFECTION 



Infection means the successful invasion of the tissues of the 

 body by either animal (protozoa, vermes) or vegetable (bacteria 

 and moulds) organisms with the evidences of their action. To 

 successfully infect the body, bacteria must enter the tissues, be 

 of sufficient number, find the tissues receptive, and continue 

 to multiply. 



The skin, mucous membranes, and the various cavities of the 

 body connected with the outside air, teem with countless bacteria 

 at all times, many of which are pathogenic, yet there is no infec- 

 tion, because the tissues are not invaded. Again, there can be no 

 doubt that highly pathogenic bacteria enter the tissues of healthy 

 people at times, in small numbers, and yet no disease is produced, 

 because of their scarcity, or by reason of the tissues not being 

 receptive. Infection implies not only invasion of the body, but 

 injury to the tissue. Certain bacteria may invade a body, and 

 yet create no harm. These bacteria may enter dead or dying 

 body tissues, and secrete poisonous substances (toxins) which 

 may be absorbed, and produce pathologic symptoms known as 

 Saprcemia. Clots of blood in the parturient uterus, and gan- 

 grenous limbs may be invaded by strict saprophytes incapable of 

 life in living tissues, and yet cause much harm by the absorption 

 of their products. 



Infestation is when organisms, even pathogenic, are present in 

 a place without exciting a reaction; the term is best used however 

 to imply the presence and action of animal parasites. Matter 

 carrying pathogenic germs is called infective. 



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