Disease Transmission and Mans Resistance 307 



true all persons do not require the same amount of sleep. Some 

 can get by with less than what is considered normal and would 

 find themselves sluggish with what others would consider to be 

 normal sleep requirements. 



OCCUPATION 

 Because of the hazards involved in certain occupations, Depart- 

 ments or Bureaus of Industrial Hygiene have sprung up on the 

 State and the National level. By determining the particular health 

 hazard involved, such Bureaus are able to institute corrective meas- 

 ures as an important phase of preventive medicine. Stone cutters, 

 for example, can breathe in a sufficient number of sharp silica 

 particles during a given time period to cause silicosis and to pre- 

 dispose the individual to pulmonary infections. So-called wet- 

 grinding and the use of protective goggles and face masks have 

 been responsible for marked reductions in silicosis. 



SPECIES, RACE, AND NATIONALITY DIFFERENCES 

 A living thing as complex as a higher animal possesses so many 

 factors which influence its resistance that it is difficult to sinojle 

 them all out. Because a horse is a horse, he does not contract 

 measles. Did you ever see a mouse with mumps? Because horses 

 and mice are members of a given species, they are not susceptible 

 to some diseases to which man falls heir, and likewise we humans 

 do not contract some diseases of lower animals. There are specific 

 diseases, however, to which both man and lower animals are sus- 

 ceptible, including tuberculosis, to mention but one disease. 



Being a member of a given race may have its advantages and 

 disadvantages with respect to susceptibility to disease. The Negro 

 appears to be highly susceptible to tuberculosis, at the same time 

 he is more resistant to malaria and to yellow fever than persons of 

 other races. American Indians have a disproportionately high rate 

 of tuberculosis. 



There is some evidence that nationality differences exist, but the 

 literature is conflicting in its conclusions. 



