548 Typhoid Fever 



skilled and the examination thorough. If, however, the 

 surface of the medium be touched with a platinum wire, it 

 is found that its entire surface is covered with a rather 

 thick, invisible layer of a sticky vegetation which the 

 microscope shows to be made up of bacilli. This is de- 

 scribed as the invisible growth. Unfortunately, it is not a 

 constant characteristic, for occasionally a typhoid bacillus 

 will show a distinct yellowish or brownish color. The 

 typical growth seems to take place only when the reaction 

 of the potato is acid. 



Bouillon. In bouillon the only change produced by 

 the growth of the bacillus is a diffuse cloudiness. 



Milk. In milk a very slight and slow acidity is pro- 

 duced. The milk is not coagulated. 



Vital Resistance. The organisms grow well at all 

 ordinary temperatures. The thermal death-point is given 

 by Sternberg as 60 C. According to Klemperer and Levy,* 

 the bacilli can remain vital for three months in distilled 

 water, though in ordinary water the commoner and more 

 vigorous saprophytes outgrow them and cause their dis- 

 appearance in a few days. There seems to be some doubt, 

 however, on this point, as Tavelf found that it lived for 

 six months in the blind terminal of a water supply pipe, 

 and Hoffmann,! after planting it in an aquarium containing 

 fish, snails, water-plants, and protozoa, was able to recover 

 it from the water after thirty-six days, and from the mud 

 in the bottom after two months. In elaborate experimental 

 studies of this question Jordan, Russell, and Zeit found 

 its longevity to be only three or four days under conditions 

 simulating as nearly as possible the conditions found in 

 nature. When buried in the upper layers of the soil, the 

 bacilli retain their vitality for nearly six months. Robert- 

 son || found that when planted in soil and occasionally fed 

 by pouring bouillon upon the surface, the typhoid bacillus 

 maintained its vitality for twelve months. He suggests 

 that it may do the same in the soil about leaky drains. 



Cold has little effect upon typhoid bacilli, for some can 

 withstand freezing and thawing several times. Observing 



* " Clinical Bacteriology." 



f "Centralbl. f. Bakt. u. Parasitenk.," xxxin, p. 166, 1903. 



J "Archiv. f. Hyg.," 1905, LII, 2, p. 208. 



"Journal of Infectious Diseases," 1904, i, p. 641. 



j| "Brit. Med. Jour.," Jan. 8, 1898. 



