78 The Story of the Bacteria 



But let an injury such as an open wound 

 occur, and the whole attitude of these leuco- 

 cytes changes. They get out of the blood- 

 vessels with all speed, in greater or less 

 numbers as the occasion may demand, and 

 gather about the edges of the wound, and after 

 a time they, together with some other cells of 

 the injured tissue, form, with the aid of the 

 blood-vessels near by, a mass of new tissues, 

 which replaces that which was lost by the 

 injury, and so permanently binds the edges 

 of the wound together. Sometimes these 

 white blood-cells gather in much greater 

 quantities about the wound than is necessary, 

 and then they are thrown off with some fluid 

 in the form of a material which we call pus. 



Now to come back to the bacteria which 

 we are studying. When these bacteria get 

 into the tissues, they may begin to grow, and 

 as they do so they produce a small amount 

 of a poison which we call a toxine. This 

 poison acting injuriously on the tissues where 

 it is formed, the white blood-cells gather about 

 it just as they would about a wound. If the 

 bacteria continue to grow and multiply, the 



