During the latter portion of the advance upon Khartum, internal disorders of various kinds were extremely common. Some of the medical staff ascribed these derangements to the use of tinned meat; but after all, the evidence of experts in England seems to show conclusively that the virulent poison called "ptomaine" is so rare, that the chance of injury from tinned meats is practically infinitesimal. Others maintained, with greater probability, that the drinking water was at fault. The native servants, to save themselves trouble or a slight wetting, invariably filled their buckets from the water close to the bank. Anyone who is acquainted with Oriental habits can realise the peril of drinking such water as this, fouled as it was by hundreds of horses, mules, and camels, and taken from a river which is treated as a vast sewer by all the inhabitants along its banks. The water question was, indeed, a big one throughout the campaign. Some filtered the muddy water as it was, but the process was a very tedious one, for the Birkfeld filter became choked with mud after about a pint of water had passed through it, and then all its internal arrangements had to be cleaned. The native servants were so stupid at any work of this sort, that one generally had to do one's filtering for oneself; and the exercise was so vigorous that, by the time one had filtered a pint, one was thirsty enough to drink a quart. Another method was to precipitate the mud to some extent by a few grains of alum; but there are hygienic reasons against the employment of this astringent in drinking water. The safest plan is to let the mud settle, and then boil the water. Yet, even if the water is boiled, one is never secure from bacteria, for fresh germs may enter it as it cools. Moreover, it is impossible to boil _all_ the water required for camp purposes; and if a servant "washes up" the plates and cups in unboiled water, or one plunges one's head into it, there can be no absolute guarantee against the intrusion of an evil bacillus into one's system. The only hope is that one's internal zeriba, so to speak, is well guarded by a valiant line of those good bacilli whose chief delight--so bacteriologists tell us--is to gather round the malignant invader and do him to death. Water taken from the middle of the stream was said to be perfectly wholesome, but even here the mud held in solution acted as an irritant. There was another little thing, too, which rather set one against any Nile water at the Atbara camp, to wit, the fact that almost every day a corpse or two of the Dervishes killed at the fight--when the Atbara was nearly empty--were caught up by the flooded stream, and carried down visibly into the Nile. Still, these bodies were almost mummified from the heat; so perhaps there was not much danger, after all, to be feared from their presence in our water supply.