The above heading sufficiently indicates a difficulty which has doubtless often occurred to those who have studied the subject of the agency of Anopheles in the causation of malaria. In some cases this difficulty has seemed so formidable that disbelief in any such agency has been boldly professed. The following observations, most of which I owe to the kindness of Dr Gould, who succeeded me at Acre in Palestine, will help to explain the occurrence of malaria at places where there would seem to be little or no breeding-ground for Anopheles, and prolonged observation by residents has not revealed the presence of the perfect insect.

A Point of great importance in medico-legal practice is the differentiation of human from other bloods. In dealing with fresh stains no difficulty has been found in distinguishing mammalian from avian and reptilian bloods. The more difficult operation of differentiating between mammalian bloods, for example between human and pig's blood, had up till the introduction of the biological, or preferably precipitin, test, except with the freshest material, baffied the ingenuity of the expert in legal medicine. In 1901 Nuttall (1. VI. '01) was amongst the first to draw attention to the possible value of this test for blood and serum in forensic practice.

An instrument which I had made several years ago presents some advantages and may therefore be of use to others who have to deal with serum-diagnosis, etc. The chief advantage of the instrument is that after each dilution has been made it is ready for making further dilutions without cleansing it. The instrument is moreover easy to manipulate. It may be described as essentially a “reversed Thoma-Zeiss pipette”, the graduations being marked upon the upper section of the tube, instead of on the lower section. The accompanying figure makes the construction of the instrument clear.

It is matter of common observation that air which is much vitiated by combustion of lighting-gas is distinctly oppressive, apart altogether from the rise of temperature which is always associated with the vitiation. This effect is always very evident if the proportion of CO2 in the air of a room has been raised to 30 or 40 volumes per 10,000 by combustion of gas. Air to which pure carbonic acid has been added in the same proportion has no such effect, however, and is practically indistinguishable from pure air. Deficiency of oxygen to such an extent as occurs in the air of a room is also without sensible effect. In coal-mines, where the air is commonly vitiated to a considerable extent by slow oxidation in the strata, it is, for instance, quite impossible to distinguish by the senses pure air from air containing an excess of 50 or even 100 volumes per 10,000 of CO2, with a correspondingly large deficiency of oxygen. The unpleasantness of air vitiated by combustion of lighting-gas is therefore not due to excess of carbonic or deficiency of oxygen.

In this paper the term B. coli is used in its most restricted sense, and as implying organisms having all the characters of the typical B. coli communis. It is a well-ascertained fact that B. coli, even when the term is so restricted, exhibit very varying virulence.