'Professor Cuica and Dr Chelarescu demonstrated to me the very heavy mortality among the A. typicus which they use in their laboratory at the institute of Professor Ballif. Eighty to ninety per.cent. deaths over a period of ten days is about the average. If this finding compares favourably with what happens in nature than at first sight it would appear that it should be extremely difficult for typicus and messeae to maintain endemic malaria but when it is remembered that numbers over a hundred can easily be collected in a single bedroom it is not so difficult to understand. It could be explained by numbers alone.'