668 MICROBIOLOGY OF DISEASES OF MAN AND DOMESTIC ANIMALS 



Human Carriers of Infection. It has been mentioned previously 

 that man is capable of carrying infectious agents when he himself is 

 not infected. For example, in the case of diphtheria it has been 

 repeatedly shown that convalescents from diphtheria, persons who 

 have had the disease, and persons who have never had the disease, 

 frequently carry the etiological microorganisms of this disease in a 

 virulent form and are accordingly exceedingly dangerous as dis- 

 seminators. Not uncommonly persons who have had typhoid fever 

 carry large numbers of virulent B. typhosus in their bodies, particularly 

 in the gall-bladder, and disseminate them through the intestinal 

 excreta thus causing many infections when this excreta comes into con- 

 tact with water used for drinking purposes or food supplies. B. 

 typhosus may be carried for many years. Asiatic cholera is occasionally 

 carried in the same way. It has also been shown that well individuals 

 may carry the etiological agents of epidemic cerebrospinal meningitis 

 and acute poliomyelitis or infantile paralysis. Individuals who carry 

 infectious organisms are popularly known as " bacilli carriers" and 

 should always be kept under rigid quarantine or observation. 



Contact Infection. It is only necessary to emphasize certain points 

 in addition to what has been said in the foregoing. It has been stated 

 that animals may communicate an infectious agent to other animals 

 of the same or different, but susceptible, species by direct contact. 

 Probably the commonest diseases to be communicated by animals to 

 each other are tuberculosis and glanders. This is commonly accom- 

 plished by the rubbing of the mouths and noses together although the 

 disease may be acquired in other ways. Among the human race the 

 diseases which are usually communicated by the contact of one indi- 

 vidual with another are diphtheria, scarlet fever, smallpox, chicken- 

 pox, mumps, measles, gonorrhea, chancroids and syphilis. In the six 

 first mentioned diseases it seems that the expirations and possibly in 

 rare instances the desquamations of the skin in those which have an 

 eruption carry the causal microorganism. The infectious agent is 

 inhaled into the nose or throat. Some of these diseases may be in 

 rare instances transmitted by intermediate agents, clothing, etc. 

 (fomites). In the last three diseases mentioned, which are known as 

 the venereal diseases, an abrasion of the integument is a prerequisite 

 and the infectious agent must enter by this route. Infection is usually 

 brought about by absolute contact of one individual with another. 



