ii8 NOTES OF A BOTANIST 
admixture of a quantity of yellowish-green slime, 
called limo. I examined the latter with the 
microscope and found it to consist chiefly of decom- 
posed Confervse, with a very few Diatoms inter- 
mixed. It originates in small lakes and sluggish 
igarapes, whose mouths, connecting them with the 
Tapajoz, become dried up in summer ; and, when 
they are reopened by the swelling rains, the limo 
which had accumulated in them whilst stagnant is 
discharged into the river. No doubt this slimy 
water is very unwholesome, and those who are 
obliged to make use of it filter or strain it as well 
as they can ; but at Santarem those who have boats 
and men send out for Amazon water, which is 
always wholesome, and apparently grows sweeter 
the longer it is kept ; whereas that of the Tapajoz, 
when at its best, is apt to acquire a sickly smell if 
kept a few days. I have seen a similar effect from 
a similar cause in the river Atabapo, a tributary of 
the Orinoco. 
Allowing its due weight to the cause thus briefly 
sketched, there is another and more important one, 
first pointed out by Humboldt, to account for the 
healthiness of the rivers of equatorial America 
which run east and west, and the unhealthiness of 
those whose course lies north and south, namely, 
that the former alone are accessible to the full force 
of the easterly or general trade wind. On the main 
Amazon, especially in the lower part, ague does not 
occur as an epidemic once in thirty years, thanks to 
the prevalent easterly wind ; yet even there we 
had sometimes, about new or full moon, a day or 
two of what is called vento da cima or " wind 
from up river" [i.e. westerly), and it is justly 
