VIBRIO CHOLERJE. 355 



stage is soon reached where the colonies appear to con- 

 sist entirely of most minute, strongly reflecting fragments, 

 looking, according to Koch, as if covered with broken 

 glass (49, II ). This is the most characteristic stage. The 

 liquefaction now rapidly advances. The peripheral parts 

 of the colonies disintegrate more and more (49, iii, v), 

 the structure appears fragmented and very granular, and 

 sometimes a hairy border is formed at the periphery (64, 

 v) or a gray transparent zone (53, iii), until finally the 

 entire colony is broken up into single fragments and small 

 portions (49, viii). Sometimes also the colonies may per- 

 sist as compact masses in the areas of liquefaction (49, 

 ix), when they are dark yellow to brown (50, iv), and 

 there even occur forms Avhich have absolutely no resem- 

 blance to cholera (50, i, ii, v). In general, the varia- 

 bility is extraordinarily great, as is sufficiently shown in 

 the illustrations (49, iv, vii; 50, iii; 53, v; 54, v, vi). 



On one occasion in a gelatin plate of vibrio aquatilis 

 irregularly formed secondary colonies, resembling those of 

 the Bact. coli, were observed, and similar ones of the 

 vibrio cholerae (53, vii) may also occur. 



Gelatin Stab. — At first thread-like and not character- 

 istic (47, i; 53, ii; 54, i). After a short time — twenty-four 

 to thirty-six hours — there occurs upon the surface of the 

 gelatin a very small perforating depression, which soon 

 extends further in the form of a large air-bubble (47, ii). 

 In the depth the liquefaction extends in the form of a 

 flattened funnel until the wall of the tube is reached (47, 

 III, rv). Later the liquefaction becomes cylindric. The 

 area of liquefaction is sometimes cloudy (47, in), some- 

 times only filled with the finest fragments (47, iv). In the 

 stab canal granular, yellowish-white masses are usually 

 implanted. It has been demonstrated by many observers 

 that freshly isolated cultures of cholera vibriones are able 

 to liquefy gelatin more vigorously than old laboratory 

 cultures; therefore one must guard against recognizing 

 rapid liquefaction of gelatin as evidence against the diag- 

 nosis of cholera. (See p. 61.) Such liquefactions as 

 shown in Plate 54, ii, in; Plate 53, i, ii; Plate 62, i, ii, are 

 very unusual, but do occur. 



Agar Plate. — (a) Natural size : Roundish, light brown- 



