During a recent tour in Roumania and Bessarabia I had the opportunity of studying some of the conditions prevailing in districts where there is much malaria and, as far as is known neither of the two chief carriers, A. labranchiae and A. elutus, occur. The variety atroparvus is very seldom found, in some of the malarous villages it has not yet been identified. The other two varieties, maculipennis maculipennis and maculipennis messeae are very plentiful. Often they appear to be about equally divided but from my observations it sometimes showed that maculipennis maculipennis far outnumbered messeae.

Recent researches seem to correlate the presence of malaria with the varieties A. elutus and A. labranchiae and, to a much less [sic] extent, A. atroparvus. More recently, districts with much malaria have come to light where only the so-called non-malarious races of A. maculipennis occur. Many districts in Northern Roumania and Bessarabia come within this category.

Dr. Hackett has recently reported some of his investigations into malaria in Russia. There they have none of the true malaria transmitters, only messeae and typicus. But there is much malaria there. There is according to him a great scarcity of cattle.

The same may be said of many of the districts which I visited in Roumania. There is much malaria, the three important transmitters are absent but it could hardly be said that there is a great scarcity of cattle. Most of the peasants appear to own at least one cow, every peasant has his pony and many of them have at least one pig. I found much interest in comparing the types of human habitations with the types of animal houses from the point of view of resting places for Anopheles maculipennis.

The houses of the peasants and even the arrangement of the beds and furniture seemed to vary but little in any district. Low ceilings, badly lighted and not well ventilated; the bed in one corner of the room and the outer covering on the bed nearly touching the floor. The sheds where the cattle are housed are of two important types, important I think from the point of view of resting places for A. maculipennis. One type consists of a square room with a thatched roof and three walls, one side being completely open. The other type is much the same except that the four sides are completely built up and the entrance to the shed is by a door at one end. At first sight this would not appear to be such a great difference but I believe is [sic] is of very great importance. It was always extremely difficult to collect even a few specimens from these three sided animal houses, even when a cow is tethered in one. On the other hand the completely shut in animal house was, in every instance, teeming with mosquitoes. If we take the three kinds of houses, (1) The three sided animal house, (2) The four sided animal house and (3) The dwelling house of the peasant, I believe that the insects prefer to live in (1) The four sided animal house (2) The house of the peasant and, (3) A bad third, the three sided animal house. I think there is little doubt that the closed up animal house conforms to something approaching the ideal resting place for both messeae and typicus and also for atroparvus. But the important point which I would like to make is that even when animals are plentiful, if the houses of the humans are found to be more suitable to the mosquitoes than is a certain type of animal house then may it not be the case that malaria remains endemic in the absence of the more important vectors because of the kind of dwellings used by man and animals. In many of the rooms of the peasants over one hundred A. maculipennis were collected, messeae and typicus forming the entire population. The over hanging bed coverings offer ideal shelter for the mosquitoes and it was often quite easy to collect twenty to thirty specimens from underneath the bed. 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. Dr. Hackett has shown that a dence [sic] population of typicus and messeae may maintain malaria in endemic form which can be explained by the absence of cattle; may it not be the case also that malaria may be maintained by the presence of numerous cattle which are so housed as to be less attractive to the mosquitoes than are the dwellings of the inhabitants?

Dr. Sicault of Morroco [sic] informs me that there they cannot induce var. labranciae to bite cattle, it is essentially and [sic] insect which selects man. The same line cannot be srawn [sic] for messeae and typicus with regard to animals. We know that in the laboratory both varieties feed readily on man. May it not happen in nature that these two varieties, while preferring perhaps the semi-dungeon like shelters under which some animals are housed, will select the habitations of man if he happens to be living in the same kind of dwelling which the insect prefers and which more closely fulfil its requirements.’