Contagioits and Epizootic Diseases. 41 



digesting and assimilating such organic matter as is pre- 

 sented to them, and in this wealiened state they are readily 

 acted upon by the hydrolytic fennent of the bacterium and 

 reduced to a soluble product which the bacterium can take 

 into its substance and assimilate. This explains why so 

 many bacteria can grow in the animal tissues that can not 

 grow in the blood. In the solid tissue the cell is fixed and 

 immovable, and must sustain the whole force of the undi- 

 luted bacteria product (alkaloid and ferment). If at all 

 susceptible to these, it is therefore liable to succumb. But 

 in the circulating blood, the constantly moving liquid speed- 

 ily dilutes and weakens the bacteria poisons, so as to fre- 

 quently render them harmless, and meanwhile the bacteria 

 tliemselves are constantly assailed by new streams of the 

 diaiesting product of the blood-globules, and are nearly 

 always weakened or even digested by the blood-globules. 

 Hence, too, the preference shown by the disease-producing 

 bacteria for the lymphatic system over the blood. In the 

 lymphatic system the circulation is slow, especially in the 

 microscopic net-works in which the lymphatics originate in 

 the tissues, and in the glands in which the lymph is delayed 

 and its cells multiplied. Here, accordingly, we have a con- 

 dition approximating to that of the cells in the solid tis- 

 sues. The comparatively stagnant lymph-cells in the radical 

 net-works and glands arc attacked by the concentrated poi- 

 sons of the bacteria, no longer diluted and weakened by the 

 active circulation of liquid that takes place in the blood- 

 vessels, and the bacteria, living and multiplying at their ex- 

 pense, invade the surrounding tissue as well, and can per- 

 haps after a time carry their invasion even into the blood 

 with good prospect of success. It should be noted that 

 even in the solid tissues an attempt is made to meet and 

 conquer the invading army of bacteria. As soon as the 

 irritant products begin to act on the tissue, inflammation is 

 set up and large numbers of the white globules of the blood 



