808 HEMOPHILUS 



or it may occur in pairs end-to-end, having a dumb-bell appearance. In size the 

 bacillus is about l-l-l-S fi long by 0-6 /n broad (Stein 1928). It may be intra 

 or extracellular in position. It does not form spores ; it is Gram-negative, and 

 non-acid-fast. In cultures on solid media the organisms appear as isolated indi- 

 viduals, in groups, and in short chains ; in fluid media very long chains are frequently 

 formed, and in certain media it produces a peUicle with dependent " stalactites " 

 of growth (Cunha 1939, 1943). 



The organisms may be cultivated by inoculating scrapings from the floor of the 

 ulcer on to a medium consisting of 3 per cent, agar contauaing 20-33 per cent, 

 defibrinated rabbit's blood : the medium should be prepared on the day of inocu- 

 lation, and should be distributed into wide tubes having a large surface exposed 

 to the air (NicoUe 1923, Reenstierna 1923, Nicolle and Durand 1924). Several 

 tubes should be inoculated, and incubated at 35° C. Colonies appear in 24 hours, 

 and may be picked off for purification. On blood agar after 24 hours the colonies 

 are circular, 0-5-1 -0 mm. in diameter, low convex, greyish-white and gUstening, 

 with a smooth svu-face and entire edge ; after 2 to 3 days, they may reach a diameter 

 of 2 mm., and the surface may show a crateriform depression. According to 

 Himt (1935), growth occurs best in sealed tubes, suggesting that it is favoured 

 by an increased partial pressure of COg. 



The necessity for blood in the medium, and a low partial oxygen pressure is 

 stressed by Sanderson and Greenblatt (1937). Watanabe (1939) confirmed the 

 necessity for blood ; rabbit blood was best, followed by that of the goat, sheep, 

 ox or man. He observed no growth stimulation by COj. 



According to LwofiF and Pirosky (1937) H. ducreyi requires X but not V factor 

 for growth. Only small quantities of hsemin are required. The growth of some 

 strains in the absence of blood or serum in the medium (Hababou-Sala 1925, de Assis 

 1926) may be attributed to the presence of small but sufficient quantities of hsemin 

 in nutrient broth. 



Another medium that is recommended for primary isolation consists of 1 part 

 of 5 per cent, glycerine agar and 4 parts of Besredka's egg medium. On this 

 medium the colonies are said to be round, transparent, and of a rose mother-of- 

 pearl colour (Hababou-Sala 1925). After preUmmary incubation at 35° C, cultures 

 are said to remain viable at room temperature for about a month. 



In Martin's broth, to which 20 per cent, of defibrinated rabbit's blood has 

 been added, the organism develops rapidly, forming granules, which are suspended 

 in the liquid or become attached to the walls of the tube. After a few days, an 

 incomplete film may form on the surface. Cultures in this medium remain viable 

 in the incubator for at least 10 days. 



For preserving the organism, it should be inoculated into a medium consisting 

 of 0-25 per cent, of nutrient agar, 1 per cent, starch, and 20 per cent, of defibrinated 

 rabbit's blood. Cultures on this medium remain ahve for a month at incubator 

 temperature, and for a similar period at room temperature, provided they are 

 previously incubated for 5 days. 



H. ducreyi is not specially resistant : it is kiUed by moist heat at 55° C. within 

 an hour, and by 0-5 per cent, phenol in a comparatively short time. 



The fermentation reactions of H. ducreyi do not appear to have received much 

 attention. Serologically, suspensions from blood-agar cultures are agglutinated 

 by a specific antiserum ; this reaction may be used for identification. 



H. ducreyi is naturally pathogenic for man. Monkeys have been successfully 

 infected. The organism has a low pathogenicity for chick embryos (Anderson 

 and Snow 1940). 



A hsemophihc organism resembhng H. canis and H. ducreyi in requiring only 

 X factor, but requiring an excess of COj in the atmosphere for its growth, has 

 been isolated from an ulcerative endocardial lesion in man (Khairat 1940). 



