MODE OF SPREAD OF INFECTIVE DISEASES. 739 



vitality for a few days under ordinary conditions ; they 

 die as the result of drying or from over-growth by sapro- 

 phytes. Hence the most frequent sources of infection 

 are the fresh dejecta, and the objects contaminated with 

 them : linen, bedding, water, food, superficial layers of 

 the soil. Multiplication can occur on various nutrient 

 materials, as in the case of typhoid bacilli. 



c. Non-contagious Facultative Parasites. 



Malaria: probably in marsh water, on the banks of 

 rivers, on the surface of marshy soil. Nothing more 

 precise is known. 



2. The Modes of Transport. 



According to the description given in the preceding Modes of 

 chapter, the sources of infection are as a rule repre- belbween the 

 sented by the fresh or dry secretions of wounds, of the 



diseased mucous membranes, or of the skin ; further, healthy 

 by objects and materials in our surroundings contami- 

 nated by them, especially dressings, linen, clothing, 

 bedding, the soil under the flooring, drinking water and 

 articles of food, the most superficial layers of the soil. 



From these sources the infective agents may be 

 carried to individuals capable of taking the infection. 



1. By contact between the healthy and sick. The 1. Contact 

 surface of the body of healthy individuals is brought 



into direct contact with the morbid secretions or the ai . c -, k i ? rtl " 



viduals. 



objects harbouring them, by handling the infected per- 

 sons, or even through a third person. Almost all the 

 infective diseases can be transported in this way. This 

 mode of transport is on the whole extremely frequent, 

 and in the case of many diseases it is the only, or at 

 least the most important, mode of infection (syphilis, 

 gonorrhoea, infective diseases of wounds, &c.). 



2. By contact with infective animals. The transmis- 2. Contact 

 sion of the most important zoonotic diseases occurs by )e wee 



