The occurrence of a peak in the true blood-sugar curve of the fasting fowl on the 3rd or 4th day, as found in previous work, was confirmed. No correlation was found to exist between this increase in blood sugar and the concentration of protein (uric acid and non-protein nitrogen) or fat (cholesterol and lecithin) metabolites in the blood, or between it and the muscle glycogen; in regard to liver glycogen and the R.Q. the results were inconclusive. After glucose ingestion the hyperglycaemic response and the rate of oxidation of sugar decreased as length of the previous fast was increased. These effects were probably due to a falling off in the rate of absorption and to utilisation of increasing proportions of absorbed sugar to restore the glycogen deposits. Adrenalin produced a greater degree of hyperglycaemia in fowls fasted for 96 hours than for shorter periods, and the corresponding liver glycogen values indicated that only about one-fourth of the extra sugar could have come from the original glycogen stores. The R.Q. during luxus absorption of carbohydrate was near or above unity, thus indicating conversion of sugar into fat. The R.Q. rapidly fell to below 0·700 and then remained steady during a fast of 7 days; the fasting quotient was not appreciably altered by protein meals or by maintenance on a protein diet, but was raised by ingestion of pure fat. Uric acid formed, during fasting, 50 per cent. or more, and after a protein meal 30 per cent. or more of the urinary nitrogen, and the low R.Q. is believed to be due to the loss of O 2 incurred in the synthesis of uric acid. The Zuntz-Schumburg tables are, therefore, inapplicable to the fowl. In fasting, ketosis did not occur, and the metabolic rate was higher in the morning than in the evening. One of us (K. M. H.) is indebted to the Medical Research Council for a personal grant.
The progress of food through the alimentary canal was studied by X-rays and the results are summarised in Fig. 12. The movements of the crop and gizzard were recorded graphically. Those of the crop did not conform to a constant type of rhythm and they were, unlike the gizzard contractions, influenced markedly by impulses from the higher centres. The fasting fowl was very sensitive to pressure changes in the crop but not to those in the gizzard. The rate of contraction of the gizzard was about 2.5 per minute and it was increased to about 3 per minute by ingestion of food irrespective of its nature. The effect of drugs on the movements of the gizzard led to the opinion that they are controlled by the vagus and sympathetic nerves. The blood-sugar of fowls was studied during fasting and after various kinds of carbohydrate-rich foods. After a preliminary fall, it rose on the third and fourth day of fasting to fall again sharply to a slightly subnormal level, about which it remained until the end of the seventh day. A change in the type of energy metabolism is suggested as the probable cause of these fluctuations. The nature of the hyperglycaemia following diets containing cellulose in varying states of division, confirmed the view, already expressed, that the gizzard functions as a filter, in such a way that fine material enters the duodenum in about I min. after ingestion while coarse material is retained much longer to be ground by the contractions of the organ. Within 5 min. after ingestion of a starchy meal the blood-sugar rose distinctly, thus suggesting correspondingly rapid hydrolysis of starch and absorption of glucose. The absorption coefficient of glucose was found to be 0.209, and evidence was obtained suggesting that there is probably an optimal solution for absorption at a concentration nearer 0.75 M than 2 M . The changes in blood-sugar and in liver glycogen corresponded with the rate at which glucose was absorbed.
The results of experiments conducted on goats and sheep by X-rays and by blood-sugar analyses have been considered with the data of other observers and the deductions outlined below have been made. Ingesta, whether liquid or solid, first enter the reticulum and rumen. Heavy matter lodges in the former and light material may enter the same cavity or the rumen. Heavy particles remain in the reticulum for several days until they are broken down, probably by maceration. Light particles move all through the reticulo-rumen at a rapid rate, but the range of movement is least in the posterior ruminal sac. The reticulo-rumen is a mixing and fermentation cavity. Mixing is caused by rhythmical waves of contraction which pass over the reticulum, dorsal sac, ventral sac and posterior sac of the rumen in this order at intervals of 40 to 80 sec., the whole cycle requiring 25 to 40 sec. Onward passage of ingesta from reticulo-rumen is probably due, chiefly to an aspiratory act on the part of the omasum, the leaves of which filter off coarse materials and, by alternating contractions, grind them, while the contraction of the viscus as a whole squeezes the fluid and fine materials into the abomasum. The fundus of the abomasum shows no gross movements, but maintains a steady pressure on its contents, and thus drives them into the pylorus which expels them by peristalsis into the duodenum. Distension of the abomasum probably prevents its overfilling by reflexly inhibiting the movements of the fore-stomachs. The essential factors causing the rejection of the food mass in rumination are (I) thoracic negative pressure produced by sudden descent of the diaphragm and closure of the glottis, (2) relaxation of the circular muscle of the cardia and its dragging forwards by extension of the head and contraction of the longitudinal oesophageal muscle, (3) contraction of the dorsal ruminal sac. A reticular contraction precedes rejection, and swallowing of the remasticated bolus just precedes the succeeding reticular contraction. The fore-stomachs attain adult form at about the 7 month. The vagus is motor and the splanchnics inhibitory to the fore-stomachs. The fore-stomachs contain food after 7 days' starvation. The fasting blood sugar varies from 63 to 86 mg. per 100 c.c., and it rises steadily from the 40th to the 169th hour of fasting. The blood sugar rises slightly but very variably after carbohydrate meals. The inconstancy is related to the X-ray findings, which showed that barium meals may remain in the reticulo-rumen for 60 min. or more, or may pass into the omasum and abomasum within 5 min. after ingestion. The percentage increase in blood sugar after carbohydrate meals is greater in fasted than in non-fasted animals.