A. Gram's Method.—Young individuals give an intense reaction with this stain; old bacilli are easily decolourised, and degenerate forms are always Gram-negative, while single individuals have been observed which showed gradation from one pole of the cell to the other.
B. Loeffler's Methylene Blue.—According to the behaviour of the organisms studied, a separation into two types appears possible, type A being uniformly impregnated, while type B shows distinct differentiation. The cell body is seen to contain a varying number of round to oval bodies or granules. This is the appearance already mentioned by Düggeli, Luerssen and Kühn, and Kuntze, and from which the granule bacillus derives its name. In opposition to the observations of Kuntze, the occurrence of granules was not found to be variable; it was, indeed, so constant as to constitute a distinguishing characteristic between the two types. The organisms of this group are difficult to cultivate, and freshly isolated growth is obtainable only on media containing whey, malt, or in milk. They grow equally well under aërobic or anaërobic conditions. The optimum temperature for growth is 113° to 115° F.; growth is fair at 85° F., slight at 75° F., and does not take place at 68° F.
Colonies on whey agar are round to irregular, greyish white, curled and filamentous, often streaming, and in a few cases smooth and even in structure. Gelatine is not liquefied. There is no surface growth on gelatine stab-cultures. Along the stab the growth is filiform, beaded, with subsequent horizontally projecting ramifications. Milk is coagulated in eight to eighteen hours at 112° F., and is the most favourable medium for growth.
[I am indebted for this group of illustrations (seventeen in number) to the editor of Bacteriotherapy, New York, U.S.A.—L.M.D.]
Fig. 30—Photo micrograph of preparation made from Yoghourt, showing yeast cells, large lactic diplococci, small slender bacilli and many large bacilli possessing the morphology of Bacillus bulgaricus. Yeast cells are almost invariably found in native Yoghourt, but do not appear to be essential to the production of a tropical beverage. Indeed, they would seem to be responsible for the unpleasant astringent taste often met with in old samples of this product.
Fig. 31—Photo micrograph of smear from Greek Curdled Milk called "Giaourti," and showing yeast cells, long bacilli and a mould (Oidium lactis), possessing very large elongate cells. The presence of the latter is very undesirable, as it rapidly combusts the lactic acid, digests the casein, and imparts a strong unpleasant cheesy flavour to the beverage.