The death of Professor von Pettenkofer, which was briefly alluded to in the last issue of the Journal of Hygiene, has removed one who was everywhere acknowledged as a great leader among the workers in our science, and as the pioneer who has been mainly instrumental in bringing about the recognition of Hygiene, particularly on its experimental side, as a separate subject of investigation and university instruction.

It is well known that fresh sewage always contains large numbers of the common colon bacillus. It is also true that when a water source is polluted with any considerable quantity of fresh sewage it is usually possible to demonstrate the presence of the colon bacillus in such water. Upon these familiar facts have been based various methods and conclusions of greater or less value to public hygiene.

Formic aldehyde, the simplest possible aldehyde, is a substance possessed of considerable biological and chemical interest. Its biological interest consists in the fact that it has long been regarded as forming the first product of plant assimilation, and has recently been actually demonstrated as such in plants. The ease with which this substance undergoes polymerisation resulting in the formation of sugars, under the influence of simple reagents, justifies the assumption that formic aldehyde is an essential link in the building-up of complex carbohydrates by plants. In addition to this it has recently been requisitioned as the only possible source of proteid anabolism. Its interest to the physiological chemist is that it combines energetically with proteids, and to a less extent with carbohydrates, effecting considerable alteration of their physical and physiological properties. This behaviour seems to be directly antagonistic to the biological rôle ascribed to the substance above. This apparent anomaly of the same substance being both a poison and an essential physiological constituent of living cells is discussed by Loew. It seems to depend upon the fact that what may be termed the biological formic aldehyde is present in small quantities (dilute solutions) and is quickly used up, owing to the ease with which it polymerises or forms innocuous compounds. This last property has an immediate bearing upon the subject of this inquiry in so far as it may serve to explain the results obtained by the administration of small quantities of formic aldehyde to man in his food. It is in this connection that formic aldehyde is of interest to us, and the importance of this subject is in our opinion sufficient to justify us in reviewing somewhat exhaustively the results of other observers with regard to the chemical and physiological properties of this substance.

During the thirteen years which have elapsed since the publication of my researches upon the bactericidal properties of the blood and other fluids of the body, a large amount of most valuable knowledge has been acquired regarding the blood both in health and disease. Through the work of many investigators the complicated subject of immunity is gradually being solved, and we are beginning to understand the way in which the body combats or is protected against the inroads of disease. We have learnt of the existence of specific antitoxic, agglutinative, haemolytic, bactericidal and cellulicidal properties in the blood-serum, etc., as also of a number of neutralizing bodies to these. The quite recent discovery of specific precipitins, which act upon various bacterial products, milks, peptone, egg-albumin, and upon human blood and its derivates, has opened a wide field for investigation, which cannot fail to ultimately yield results of the greatest importance. We have to thank bacteriological investigation for the greater part of the advances which have been made, although a considerable portion properly belongs in the domain of physiology.

The Graphic Method, which I first used in connection with the outbreak of milk-carried enteric fever which occurred in Clifton in 1897, is here applied to a similar outbreak of milk-carried scarlet fever.

It will be accepted that milk containing large numbers of bacteria, as well as the products of their growth, is less suitable for food than unpolluted milk. A bacteriological examination of the milk in great cities generally will show that much of it in hot weather, and some of it at all seasons of the year, abounds in bacteria. Clinical experience also teaches that much of the milk in hot weather is unsuitable for food, especially for infants; because in them, owing to the rapidity with which the milk passes through the stomach, gastric digestion is almost no safeguard against the entrance of disturbing microorganisms into the intestines. Even pasteurization of milk charged with bacteria and their products does not restore it to its original condition, for the dead bodies of the bacteria and their toxins still remain. The changes in milk which are most deleterious being now known to be due to bacteria, it is theoretically conceded by all, that commercial cow's milk, the substitute for maternal milk, should be as nearly free as practicable from bacteria.