IN THE TROPICS. 
•29 
foreign micro-organisms. Of the different well-known 
sterilization methods, it is, as a rule, sufficient for mycologi- 
cal purposes in the tropics to use the so-called fractional 
method, which was invented by Tyndall — the boiling of 
the nutritive medium four or five times, with an interval of 
one or two days between each two operations. This, how- 
ever, is not always sufficient for the above-mentioned palm 
sugar solutions. A bacterium occurs regularly in the 
solution of Arenga (not of Caryota)"^' sugar, which has a 
great similarity to the common hay bacillus, and which is 
distinguished by the great capacity of resistance of its 
germs. It is particularly resistant to heat, and makes the 
sterilization of the solutions — a necessary preparation for 
the success of mycological cultures— very difficult. I 
endeavoured repeatedly to confine myself to the convenient 
fractional sterilization method. Although the boiling in 
glass flasks was repeated for several weeks, and the tem- 
perature raised to 100° C. on the first occasion, I was not 
successful in attaining my object — the bacteria appeared 
again and again, and as there were no other organisms to 
affect their successful growth, they soon took possession of 
the entire fluid and made it quite unsuited for cultures. 
The other micro-organisms, though at first often present 
in large quantity, were more sensitive to outside influences, 
and a heating three or four times repeated in four or five 
days was enough to kill them. 
In the case of the nutritive solution under consideration 
it is in general best to kill the resistant spores of the 
bacteria by heating to about 110° R. in an autoclave. After 
this process has been once employed, it will suffice to 
employ a fractionated sterilization to 70° R. for the three or 
four further heatings. The solution can indeed be easily 
freed from all germs by an immediate heating and the first 
necessity for a pure culture be thus obtained, but experience 
shows that its nutritive capacity is thus seriously lessened. 
For clearness’ sake I repeat of Arenga (not of Caryota). 
