BACTERIA AND DISEASE 2JI 



results will follow, especially if the bacteria are present in 

 sufficient numbers, or meet with devitalised, and therefore 

 non-resisting, tissues. 



These, then, are the five possible ways in which germs 

 gain access to the body tissues. The question now arises, 

 How do bacteria, having obtained entrance, set up the pro- 

 cess of disease ? For a long time pathologists looked upon 

 the action of these microscopic parasites in the body as 

 similar to, if not identical with, the larger parasites some- 

 times infesting the human body. Their work was viewed 

 as a devouring of the tissues of the body. Now, it is well 

 known that, however much or little of this may be done, 

 the specific action of pathogenic bacteria is of a different 

 nature. It is twofold. We have the action of the bacteria 

 themselves, and also of their products or toxins. In par- 

 ticular diseases, now one and now the other property comes 

 to the front. In bacterial diseases affecting or being trans- 

 mitted mostly by the blood, it is the toxins which act 

 chiefly. The convenient term infection is applied to those 

 conditions in which there has been a multiplication of living 

 organisms after they have entered the body, the word in- 

 toxication indicating a condition of poisoning brought about 

 by their products. It will be apparent at once that we may 

 have both these conditions present, the former before the 

 latter, and the latter following as a direct effect of the 

 former. Until intoxication occurs there may be few or no 

 symptoms, but directly enough bacteria are present to pro- 

 duce in the body certain poisons in sufficient amount to 

 result in more or less marked tissue change, then the symp- 

 toms of that tissue change appear. This period of latency 

 between infection and the appearance of the disease is 

 known as the incubation period. Take typhoid, for example. 

 A man drinks a typhoid-polluted water. For about four- 

 teen days the bacilli are making headway in his body with- 

 out his being aware of it. But at the end of that incubation 



