526 MICROBIOLOGY OF THE DISEASES OF MAN AND ANIMALS. 



they do not multiply in the soil. They may exist as ordinary saprophytes. 

 The microorganisms of typhoid and cholera have been known to remain 

 alive for a year or more in soils containing large quantities of organic 

 matter. The various pyogenic micrococci are also occasionally found in 

 the soil and may enter the body of man and animals through wounds. 

 These last-mentioned organisms may live for indefinite periods of time 

 on the skin and only enter the body when the resistance of some tissue 

 is lowered. 



INFECTIONS FROM FOOD. Quite a large variety of pathogenic micro- 

 organisms have been found in the various food products. Milk is perhaps 

 the most common food product to be infected. The causal agents of 

 diphtheria, scarlet fever and some other diseases are disseminated by 

 means of milk. Milk having been contaminated by water containing B. 

 typhosus may be the means of conveying typhoid fever, and the dissemi- 

 nation of Malta fever is accomplished by the drinking of the milk of in- 

 fected goats. Typhoid fever has also been known to have been acquired 

 from the eating of vegetables which have been washed in water containing 

 the pathogens. Oysters and various shell-fish have carried the causal 

 microbic agents of typhoid and Asiatic cholera. Three infections coming 

 from meat sometimes occur, namely, botulism, enteritidis infections and 

 para-typhoid fever. In these instances the causal microorganisms are in 

 the meat. Another type of meat poisoning also occurs from the eating of 

 meat or fish which has been acted upon by saprophytic bacteria and the 

 proteins split up into toxic substances. 



ANIMAL CARRIERS OF INFECTION. Animals may communicate patho- 

 genic microorganisms to one another and to man in three ways, namely, 

 first, by direct or indirect contact; second, by serving as mechanical carriers 

 from one individual to another; and third, by serving as intermediate hosts 

 for the pathogen. As an example of the first may be mentioned the fact 

 that tuberculosis has been communicated from cattle to man, that 

 glanders has been communicated from horses to man and that anthrax 

 has been communicated from sheep to man by contact. The cat, while 

 not suffering from true diphtheria, seems to be able to transmit this 

 infection to the human. Under the second, the mechanical carrying 

 of an infection, the insects are principally concerned. It is demon- 

 strated that common flies frequently carry B. typhosus on their feet 

 from the infected patient or the excreta and deposit them on the 

 food materials thus causing infection when the food is eaten. The 



