5. As far as our present knowledge goes, it appears that infection takes place chiefly, if not entirely, by means of the latex in the field-vessels. It may take place during transport also, or even during coagulation.
6. While it is certain that infection can be caused by contact, it has not yet been shown that infection of the finished wet rubber takes place in the drying-houses by means of air-borne spores—at least, under ordinary drying conditions.
7. There is reason to believe that no further infection takes place once the rubber is well into the drying stage, and that dry rubber is not infected even by contact. From this one might infer that, as long as rubber remains dry, infection cannot take place during the voyage to the port of consignment.
8. Coloured spots do not appear until the rubber is about half dry, because that period is necessary for the development of the fungus to that stage in its life-history when it excretes colouring matter. The fungus in its earlier and colourless stage may have been present from the time the latex entered the cup.
9. The natural habitat of the fungi would appear to be decaying vegetable matter in the field.
10. Finally, if it is found impossible to be rid of fungoid-spot disease after having exercised all care and observed all known precautions, nothing remains but to supersede the ordinary drying process by some system of quick drying, such as the vacuum-drying process or a hot-air draught system, in which the rubber dries so quickly that any possibility of appearance of “spots” is entirely removed.
Surface Moulds or Mildews on Crepe Rubber.—Defects of this nature are most uncommon in the higher grades of crepe rubber, but cases of affection in the lower grades are not rare.
It will be evident from all previous discussions that the incidence of these moulds must be due to an extremely slow rate of drying. The necessary conditions would be supplied by one or more of the following causes:
(a) Making the crepe too thick.
(b) Hanging the crepe in a badly ventilated or badly situated building.