326 BULLETIN No. 161 [November, 



the 8 1st, I23cl and I7ist days of the exposure to sunshine showed 

 the tubercle bacilli to be dead or at least not sufficiently virulent to 

 produce tuberculosis when the centrifuge sediment was injected sub- 

 cutaneously into guinea pigs. 



It thus appears from these tests that pure cultures of bovine 

 tubercle bacilli, when mixed with cow manure and exposed in an 

 open place in a pasture field, remained alive in this instance for ap- 

 proximately two months. 



Exposed in the Shade. The part of the artificially infected 

 manure exposed in a place protected from sunshine was tested on 

 the same days and in the same manner as was the part exposed 

 in the sunshine. These results are given in Table 14. The parts 

 tested on the 7th, i6th, 3ist and 49th days were shown at each 

 testing to contain virulent tubercle bacilli. The infection of the 

 guinea pigs in the first two tests was severe. The guinea pigs in- 

 oculated with samples taken on the 3ist and 49th days of the 

 exposure were infected with tuberculosis but not so severely as 

 the guinea pigs inoculated on the 7th and i6th days. However, 

 they were much more severely infected than the guinea pigs in- 

 oculated with the sample taken from the part exposed in the sun- 

 shine and tested upon the same days. The three samples taken 

 on the 8 ist, I23d and I7ist days were shown not to contain viru- 

 lent tubercle bacilli. Three of the guinea pigs inoculated with the 

 first two samples remained healthy until killed on the 49th and 

 55th days respectively after inoculation of the sample. One of 

 the two guinea pigs inoculated with the sample taken on the 8ist 

 day died five days later with an acute infection. The two guinea 

 pigs inoculated with the sample taken on the I7ist day died of 

 acute infection with no evidence of tuberculosis. 



From these tests it appears that tubercle bacilli mixed with 

 cow manure remain virulent to guinea pigs for 49 days after ex- 

 posure in a place protected from the sun. All tests made later 

 than this date showed these organisms to have lost their virulence. 

 Virulence was retained longer in the shade than in the sunshine, 

 as shown by the production of more severe tuberculosis in the 

 guinea pigs inoculated from samples exposed in the shade than that 

 produced in the guinea pigs inoculated on the same days with sam- 

 ples exposed in the sunshine. 



