94 SAPROPHYTISM, PARASITISM, AND PATHOGENISM 



of cholera infantum, and, rarely, Asiatic cholera as well, all may be 

 transmitted from milk. 



Shell-fish, particularly oysters, have been known to transmit enteric 

 diseases. This has been due, in the past, largely to their exposure 

 in the estuaries of rivers where sewage flowed freely over them. 

 Typhoid bacilli enter the mantle cavity of the shell-fish, remain alive 

 there and enter the digestive tract in a viable state when the shell- 

 fish are consumed in an uncooked condition. 



Meats, particularly from beef and swine, have been known to transmit 

 paratyphoid fever, botulismus (sausage poisoning) and meat-poisoning 

 as well. There is, in addition, a group of cases with somewhat insidious 

 symptoms, which are probably due to the consumption of food, par- 

 ticularly meat, which has been decomposed by saprophytic bacteria. 



5. Animal Carriers. The microbic diseases which are transmissible 

 to man from animals and from man to man by animals are varied 

 in character. They comprise protozoan and bacterial infections and 

 the so-called " filterable viruses." Of these diseases, comparatively 

 few are common to man and animals. Microorganisms may be trans- 

 mitted to man by animal carriers in at least four distinct ways: 



(a) By direct contact. 



(b) By indirect transfer. 



(c) By mechanical transfer. 



(d) By intermediary hosts. 



(a) Direct Contact. The transfer of glanders from the horse to 

 man, of anthrax from cattle and sheep to man and of hydrophobia 

 from dogs to man represents direct transfer of the virus from the sick 

 animal to the well man. Other diseases are thus transmitted, but the 

 examples given suffice for illustration. 



(b) Indirect Transfer. Insects are common carriers in the indirect 

 transmission of the virus of disease from man to man. Flies are known 

 to have carried typhoid bacilli from typhoid dejecta to milk or other 

 food, which in turn has been consumed by man, resulting in infection. 

 The same insect, doubtless, when conditions are favorable, can and 

 does carry other enteric bacteria paratyphoid, dysentery and even 

 cholera organisms. It is very probable that other insects also par- 

 ticipate in the indirect transmission of bacteria. Acute conjunctivitis, 

 particularly that form which is prevalent in Egypt, is supposed to 

 be spread in this manner. 



(c) Mechanical Transfer. Suctorial insects are known to transmit 

 the viruses of certain diseases which circulate in the blood stream of 



