Bacteriology and Its Significance 39 



III. Infection through the Respiratory Tract. Examples of this 

 method of infection are: pneumonic plague, pulmonary tuberculosis, in- 

 fluenza, etc. These are infections mainly transmitted through "infective 

 droplets" and "from hand to mouth". This fact was again clearly 

 shown during the last influenza pandemic. An untold amount of suffer- 

 ing, incapacitation, loss of time and money can be avoided by simply 

 guarding against these last two methods of infection ("infective drop- 

 lets" and "from hand to mouth"). It is recognized that by far the 

 greatest per cent of all infections gain entrance into the body in this way. 



IV. Infection through Wounds. In this connection we must con- 

 sider wounds as ranging all the way from slight abrasions to profound 

 injuries. Slight cuts, accidents and minor operations many times neces- 

 sitate no particular precautions, but there is always danger of an in- 

 fection. Major accidents, such as bones crushed, are very productive 

 of infection. 



V. Infection through Insects. This source of infection was formerly 

 altogether disregarded but it is now considered very important. The 

 insect may play the part of a passive carrier (non-blood sucking), as the 

 mechanical carrying of infective material by flies. The insect may 

 also make its own wound (puncture) in which case it is blood sucking 

 and is an active carrier of the disease. Malaria and yellow fever, as is 

 well known, are examples of the latter method of infection. 



VI. Congenital Transmission of Disease. Here the organism enters 

 the body previous to birth, is present and active in the new born. In 

 the latter eighties almost conclusive proof was given of anthrax passing 

 from an infected cow to the calf and so spread. This was disregarded 

 at the time because it was then held that uninjured tissue could not be 

 penetrated by infective organisms. This view, of course, is no longer 

 held. Especially in syphilis and tuberculosis scores of the still born 

 show this infection. 



Avenues of Exit. 



Having thus briefly described the natural methods of infection one 

 quite instinctively asks how do germs leave the infected body. 



Micro-organisms make their exit in the secretions and through the 

 excretions. The organisms usually tend to localize in certain organs, 

 e. g., the typhoid bacillus in the kidneys, others in the liver, mammary 

 gland, etc. 



I. Saliva and Sputum. In hydrophobia (rabies) the salivary glands 

 of the animal are infected and this is the chief manner of exit. 



Tuberculosis is the most noted case of exit via the sputum. Pneu- 

 monic plague, pneumonia and influenza also are examples of the same. 



II. Nasal Discharge. The organisms causing influenza, leprosy, 

 glanders, infantile paralysis and meningitis are found in such discharges. 



III. Intestinal Discharge. This is often the chief and only avenue 

 of exit. It is primarily of importance when the organism is multiplying 

 in the intestine, but also when the intestine is penetrated, ulcerated, 

 or the growth is localized as may be the case in anthi'ax, bacillary as 

 well as amoebic dysentery, typhoid and para-typhoid fever. 



IV. Urine. It is almost axiomatic that infections of the blood 



