364 BULLETIN No. 161 [November, 



GENERAL, DISCUSSION 



A summary of the results of the experimental work is given 

 in Table 34. It is seen from this table that tubercle bacilli in pure 

 culture, spread in thin layers on sterile glazed paper slips and ex- 

 posed to the direct rays of the sun, are killed in a very short time 

 (i to 4 minutes). In this respect tubercle bacilli may be classed 

 with other nonspore-bearing organisms. When exposed to desic- 

 cation, pure cultures of these germs in thin layers are found to be 

 dead in a few days. In sputum and other foul material they appear 

 to live longer than the other 'nonspore-bearers. They are known 

 to live long enough to be blown around so that the inhalation of 

 dried sputum dust causes tuberculosis in test animals. Just how 

 frequently people are infected by breathing dried tuberculous ma- 

 terial has been discussed (see page 270). That sunlight plays an 

 important part in the disinfection of this dried tuberculous dust 

 is evident. Also that our homes, factories, and places of business 

 should have an abundance of window space, located so as to admit 

 the light, is another timely lesson. 



Tubercle bacilli in cow manure lived 73 days when a pure cul- 

 ture-mixed in a sample of manure was exposed to weather condi- 

 tions in a pasture field in the shade, and as long as 49 days when 

 exposed in the sunshine. The sample from a tuberculous cow was 

 dead at the first test, made 13 days after exposure. We were dis- 

 appointed in not being able to repeat these experiments. It would 

 be advisable to repeat this work, especially with naturally infected 

 manure from several tuberculous cows that were known to be 

 expelling tubercle bacilli per rectum. Keep pigs from three to four 

 months old in a pasture with such tuberculous cows, and allow the 

 pigs to feed upon the cow dung. Feed other pigs by mixing with 

 their feed tuberculous manure which had remained in this pasture 

 for varying intervals of time. An examination of the internal or- 

 gans of these shoats would give valuable information both as to 

 the infectiveness of the cow manure and to the length of time that 

 tubercle bacilli remain alive in such manure. This would indicate, 

 much more completely than our experiments, the length of time 

 that stock should be kept from a field in which tuberculous cattle 

 had been pastured. 



When tubercle bacilli, either in manure or in dead tuberculous 

 animals, become mixed in the soil, the danger may be still greater, 

 depending upon the opportunity for hogs to take this material 

 along with their food. The bacilli live longer under these condi- 

 tions, but the opportunity of being taken is usually less. 



The danger of man becoming infected with tuberculosis from 

 drinking water has been discussed (see page 307). Just how likely 



