Our illness may partly have arisen from another cause.  One kind of cassava (Jatropha maligna) is known to be, in its raw state, poisonous, but by boiling it carefully in two waters, which must be thrown off, the poison is extracted and the cassava rendered fit for food.  The poisonous sort is easily known by raising a bit of the bark of the root, and putting the tongue to it.  A bitter taste shows poison, but it is probable that even the sweet kind contains an injurious principle.  The sap, which, like that of our potatoes, is injurious as an article of food, is used in the “Pepper-pot” of the West Indies, under the name of “Cassereep,” as a perfect preservative of meat.  This juice put into an earthen vessel with a little water and Chili pepper is said to keep meat, that is immersed in it, good for a great length of time; even for years.  No iron or steel must touch the mixture, or it will become sour.  This “Pepper-pot,” of which we first heard from the late Archbishop Whately, is a most economical meat-safe in a hot climate; any beef, mutton, pork, or fowl that may be left at dinner, if put into the mixture and a little fresh cassereep added, keeps perfectly, though otherwise the heat of the climate or flies would spoil it.  Our cook, however, boiled the cassava root as he was in the habit of cooking meat, namely, by filling the pot with it, and then pouring in water, which he allowed to stand on the fire until it had become absorbed and boiled away.  This method did not expel the poisonous properties of the root, or render it wholesome; for, notwithstanding our systematic caution in purchasing only the harmless sort, we suffered daily from its effects, and it was only just before the end of our trip that this pernicious mode of boiling it was discovered by us.

In ascending 3000 feet from the lowlands to the highlands, or on reaching the low valley of the Shire from the higher grounds, the change of climate was very marked.  The heat was oppressive below, the thermometer standing at from 84 degrees to 103 degrees in the shade; and our spirits were as dull and languid as they had been exhilarated on the heights in a temperature cooler by some 20 degrees.  The water of the river was sometimes 84 degrees or higher, whilst that we had been drinking in the hill streams was only 65 degrees.

It was found necessary to send two of our number across from the Shire to Tette; and Dr. Kirk, with guides from Chibisa, and accompanied by Mr. Rae, the engineer, accomplished the journey.  We had found the country to the north and east so very well watered, that no difficulty was anticipated in this respect in a march of less than a hundred miles; but on this occasion our friends suffered severely.  The little water to be had at this time of the year, by digging in the beds of dry watercourses, was so brackish as to increase thirst—­some of the natives indeed were making salt from it; and when at long intervals a less brackish supply was found, it was nauseous