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THE discovery that American foul brood was a distinct disease caused by a spore-forming bacillus was first made by White (B), though Maassen (4), working independently, came to the same conclusion shortly afterwards. White termed the causal organism Bacillus larvae, and this designation was subsequently accepted by Maassen. Maassen (4) produced American foul brood in colonies of bees by feeding them pure cultures of B.larvae, but it is not clear whether his cultures contained only the vegetative cells of this organism or the spores as well. Later@) he found that B. larvae rapidly loses virulence and ability to form spores when cultivated for some time on laboratory media. w h i t e ( 1 3 ) produced American foul brood by feeding spore-containing brood filtrate or eggagar cultures of B. larvae to the bees of healthy colonies, but he does not record that disease was produced by feeding the vegetative cells of this organism alone. He also found that direct inoculation of larvae with cultures of the causal organism rarely produced the disease. In France, Toumanoff(ll) failed in his attempts to produce American foul brood by individual feeding of the young larvae of a healthy colony of bees with large numbers of the vegetative cells of B. larvae, and Chalmers(1) also experienced difficulty in infecting colonies with pure cultures of this organism. Sturtevant(7) showed that, normally, a healthy colony of bees will not contract American foul brood unless the bees are fed at least 50 million spores of B. larvae, obtained from the scales of dead larvae, in 1 litre of sugar syrup. In his experiments individual larvae did not contract the disease unIess they were fed 10 million or more spores of this organism in 0.01 C.C. of a p p .When considered collectively, the above results indicate that the vegetative cells of B. Zurvae do not cause American foul brood readily, if at all; that the spores of this species are effective in producing the disease only when introduced in large numbers into healthy colonies; that the

NONE of the numerous investigators who have studied the formation of hydrogen sulphide by bacteria has thoroughly analysed the relation between the organic sulphur-containing substrate employed and the formation of this compound. Furthermore, the failure to eliminate bacterial multiplication may have obscured to some extent the simple formation of hydrogen sulphide.Sasaki and Otsuka [1912] found that most of a large number of bacteria studied by them formed hydrogen sulphide when cultivated in Frankel's artificial medium to which either cystine or sulphur had been added. Certain of the strains investigated formed this gas from thiosulphate, only a few formed it from sulphite, and none produced it from taurine or from sulphate. Burger [1914] found that the bacteria which he studied formed hydrogen sulphide from cystine but not from taurine. Tanner [1917], employing Frankel's medium, studied a very large number of cultures and found that most of these formed hydrogen sulphide from peptone and from cystine, some from thiosulphate and thiourea, and that none of the strains formed this gas from 2-thiohydantoin, sulphite or sulphate. Almy and James [1926] showed that, when P. vulgaris was grown in a peptone solution containing added cystine, all the sulphur of this amino-acid could be recovered as hydrogen sulphide. Hydrogen sulphide was formed in cultures of this organism under both anaerobic and aerobic conditions. Tarr [1933] showed that washed cells of P. vulgaris decomposed cystine completely under anaerobic conditions, with the formation of two molecules each of hydrogen sulphide, ammonia, acetic and formic acids.In the present investigation it has been shown that the process of hydrogen sulphide formation by washed cells of certain heterotrophic bacteria is enzymic in nature, a relatively high degree of specificity existing between the structure of the organic molecule attacked and the production of hydrogen sulphide. A study of certain well-known bacterial species has been made in order to determine the distribution of the enzyme concerned; and one factor which stimulates its formation in the bacterial cell has been found. EXPERIMENTAL.Many of the substances used, viz. glutathione (oxidised and reduced forms), cystine, cysteine hydrochloride, glycylcysteine, N-acetylcysteine, N-acetylcysteine, methyl and propyl esters, S-ethylcysteine, S-benzylcysteine, methionine, 1 1851 Exhibition

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