BACILLI OF THE COLON-TYPHOID-DYSENTERY GROUP 707 



spoken of as the paradysentery bacilli. Differentiation between the 

 four types can be made by sugar fermentations as follows: 



+ = acid (no gas) . 



The Shiga bacillus also is the only one of these fixed types which does 

 not produce indol. We do not believe, as we did before, that these 

 types represent all possible variants of the dysentery bacilli. During 

 the recent war epidemics, we ourselves, as well as many others, isolated 

 non-motile, Gram-negative bacilli from the stools of mild dysentaroid 

 cases which presented cultural peculiarities and did not agglutinate with 

 the type sera, and many organisms have been described by various 

 observers which do not fit in with any of the main sub-divisions. 



Resistance of Dysentery Bacilli. Not being spore bearers, dysen- 

 tery bacilli are not very resistant to heat and chemicals. They are 

 destroyed at 60 within ten minutes, and the usual strength of the com- 

 mon chemical disinfectants kill them. Their resistance to the ordinary 

 conditions in nature is, of course, the important feature of the epidemi- 

 ology of the disease. Accordingly, a considerable amount of research 

 has been done on these problems. We quote the following facts from 

 Vincent and Muratet. 17 In garden soil they have been known to live 

 from six to fifteen days, and up to forty-nine days at a depth of 12 inches. 

 In damp sand they have been known to live as long as thirty-nine days. 

 Cultures in broth have lived for twenty-five days, and they have lived 

 more than thirty days in dejecta buried in the soil, and on linen folded 

 up. In ice, they may live for longer than a month. Exposure to sun- 

 light of course destroys them rapidly. We would like to remark in 

 connection with the viability of all organisms outside the animal body, 

 that such statements must always be limited to the peculiar conditions of 

 symbiosis, light, moisture, temperature', etc., existing under the particular 

 conditions investigated. If we remember that non-spore bearing organ- 

 isms, like the typhoid, the dysentery bacilli, etc., can be kept alive for 

 very long periods if young agar growths are kept in sealed jars in a cool 

 dark place, we may understand that under peculiarly favorable conditions 



17 Vincent and Muratet, Military Med. Manual, Univ. of London Press, 1917, 



