BACTERIA 23 



moment. Thus, it is said that about 90 per cent of all adult 

 Europeans have at one time or another been afflicted with 

 tuberculosis, although only 15 per cent die of the disease. 

 There is no doubt that every one of us has many times taken 

 the tubercle bacteria into his throat and lungs ; but if they 

 were not too numerous, and if we were in vigorous health, 

 the bacteria were quickly killed and no harm resulted. Al- 

 though tuberculosis most commonly affects the lungs, it oc- 

 curs also in the skin, in the spinal column, the hip joint, the 

 glands of the neck, the intestines, and the brain. 



35. Tuberculosis in Cattle. Tuberculosis is a disease of 

 some of the lower animals, including cattle, as well as of man. 

 The bacteria pass into the milk of diseased cows, and it has 

 been shown that tuberculosis may be conveyed to babies by 

 such milk. This is one reason for the adoption of laws by 

 various states requiring the testing of cattle for tuberculosis 

 and the killing of those found to be diseased. There is also 

 a possibility of getting the disease by eating the flesh of 

 affected cattle, but since most of the bacteria are killed in the 

 cooking of the meat, this danger is not so serious as is that 

 from milk. 



36. How Tuberculosis is Spread. The bacteria enter the 

 body by being breathed into the lungs, or by being taken into 

 the stomach with food, or through a wound. The first method 

 is probably by far the most common. The disease germs are 

 distributed in the sputum of diseased persons. If, therefore, 

 all the sputum were destroyed, the spread of the disease would 

 be very largely checked, and the immediate destruction of 

 the sputum is one of the most important means to be used in 

 combating tuberculosis. If it is not destroyed but is allowed 

 to dry, the bacterial cells also become dry and are carried 

 about like dust in currents of air (see Fig. 10). In this dried 

 condition the germs can live for a long time. They are 

 killed, however, by prolonged exposure to sunlight, and they 

 live longer in bad air, as in close, poorly ventilated rooms, 



