A short synopsis is given of previous investigation of the capillaries of children and infants in health and disease as seen under the microscope. A satisfactory method of examination of the capillaries of infants is described,and also the normal capillary formation and blood flow in these subjects. Observations on the abnormal state of the capillary circulation in dehydrated infants are set down in detail,and in addition the effect of the intravenous injection of whole blood and of dextrose solution. A discussion follows on the significance of the observations.