It is now generally accepted that the increased rate of weight gain in chicks receiving dietary antibiotics depends largely, if not entirely, on consequent modification of the microbial population of the chick's alimentary tract. Fundamental investigation of the phenomenon, therefore, calls for the maintenance of chicks free from indigenous organisms so that a defined flora can be introduced as desired. We deal here with experiments on the rearing of chicks in the Gustafsson (1948, 1959) germ-free apparatus and the effects of dietary penicillin on chick growth in germ-free or conventional environments. E X P E R I M E N T A LChicks. The chicks were produced on our own premises from Light Sussex hens crossed with Rhode Island Red cocks, so that the sexes were distinguishable at hatching by down colour. For much of this work the hens were housed in batteries and artificially inseminated twice weekly, fouling of the egg-shells being thus avoided as far as possible. On some occasions the hens were flock-mated in fold units on grass; some of the eggs from these birds were soiled, and only the cleanest were selected for the production of germ-free chicks.Gerrn-free apparatus. Three of the small light-weight tanks (see P1. I ) designed by Gustafsson (1959) and supplied by Wojidkow and Co. A. B., Malmo, Sweden, were used. The tank consists essentially of a stainless steel box, 34 in. long, 18 in. wide and 20 in. deep, covered by a plate-glass window. Into one of the sides a pair of heavy rubber sleeves is sealed, to which can be fitted rubber gloves of any suitable pattern. A third sleeve is provided on the opposite side. At one comer of the tank is a stainlesssteel U-trap to be filled with germicide, through which objects can be passed into or out of the tank. The air supply is sterilized by passing it through a steel cylinder containing granulated carborundum heated electrically to 3 50"; it is cooled by passing through a tube along the side of the tank. The exhaust air is similarly treated in order to destroy any organisms that may, deliberately or accidentally, have been introduced into the apparatus. In the experiments described here air was passed into the tanks at the rate of 7l./min during the hatching period, and subsequently the flow was increased to 10 l./min. Positive pressure was always maintained in the tanks. M. E. COATES AND OTHERS I963The apparatus was originally designed for rats; small modifications had to be made to meet the more exacting environmental requirements of young chicks. During the hatching period a relative humidity of about 65 % is optimal and was achieved by dripping water slowly into the air-intake tube as it entered the air sterilizer. After hatching, ordinary atmospheric air was supplied through the sterilizer until the birds were 2-3 weeks old, by which time humidity in the tanks began to rise because of the chicks' respiration and of evaporation from droppings and water troughs. At this timethe air entering the tanks was dehumidified bypassing it over a freezing coil at -j' bef...

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EVIDENcE has recently been advanced of the existence of afferent fibres from the abdomen in the splanchnic nerves [Bain, Irving and McSwiney, 1935]. It is also believed that afferent fibres from the abdomen are present in the vagus nerves, but the evidence in support of the presence of these fibres is unsatisfactory, and in many instances the experimental results reported are contradictory. Thus on the one hand it is stated that there is no evidence for the presence of sensory fibres in the abdominal vagus nerves [Muller, 1911]; while other investigators, working on dogs, have found that when all afferent pathways except the vagi have been eliminated, the abdominal viscera still remain sensitive [Lebedenko and Brjussowa, 1930].Histological studies of the abdominal vagus nerves have been made by Edgeworth [1892], Muller [1911], van Gehuchten and Molhant [1911], and Chase and Ranson [1914]. Heinbecker and O'Leary [1933] have studied the time of conduction of impulses in the vagus nerve, and are of the opinion that all the afferent fibres of the nerve are medullated fibres of the somatic type. Edgeworth also describes large medullated fibres in the abdominal vagus nerves which he regards as sensory in function, but he considers it unlikely that these are the sole sensory fibres in the vagus.Examination of the literature reveals the fact that while a number of investigators have obtained evidence of afferent fibres in the vagus trunks of the abdomen, few of these have set out definitely to investigate the course and pathway of these fibres. The study of afferent fibres in the vagus trunks of the abdomen in all instances has depended upon the elicitation of some reflex response in the animal.

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