Traditionally, lactobacilli have been considered the principal cause of caries, but recent findings have questioned this concept. Orland ( 1 ) succeeded in producing experimental caries by infecting gnotobiotic rats with a strain of streptococcus. More recently, Fitzgerald et a1 ( 2 ) confirmed these findings, and Fitzgerald and Keyes (3) established the cariogenicity of another strain of streptococcus in hamsters. These 2 strains of streptococci were shown to be host-specific with regard to cariogenicity: the hamster strain (designated HS1) produced caries only in the hamster and not in the rat, and the rat strain (designated FA1) produced caries in the rat and not in the hamster. Fitzgerald and Keyes also demonstrated that experimental dental caries in animals is an infectious and contagious pathological state which could be transmitted from mother to young. *Aided by research grant DE 01519, Nat. Inst. Dental Res., U.S.P.H.S. Studies of cultures from human caries have brought out evidence for the presence of streptococci similar to the HS1 and FA1 strains.Preliminary findings indicate that the human streptococci similar to the HS1 strain may be causally associated with human caries. Studies related to human streptococci similar to FA1 strains are being investigated.Materials and methods. Collection of specimens from human carious lesions. A sterile spoon excavator was used to remove carious material from the depths of lesions in both enamel and dentine from human teeth in situ.This material was inoculated in Todd-Hewitt broth, supplemented with 0.5% lactalbumin hydrolysate and incubated at 37°C for 18-24 hours.Production of antiserum. Rabbits were immunized with a vaccine prepared from heatkilled streptococcal cultures (60OC for 1 hr). The bacterial suspensions were washed twice in saline and adjusted to the density of the

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THE EFFECTS of normal aging on cerebral circulatory physiology are of interest for several reasons. Many of the disease states in which cerebral vascular and metabolic functions are studied are commoner in middle-aged and elderly persons, making statistical comparisons with normal groups, presently comprised almost entirely of young subjects, inaccurate. In addition, the alterations which occur in cerebral circulatory functions with advancing age may provide additional clues to the understanding of many clinical problems of the aged, particularly those related to vascular disease of the brain; and such studies may provide the physiologist with further information concerning general patterns of circulation in subjects of middle and old age. The purpose of this report is to record our observations in the use of the nitrous oxide technique for measuring cerebral blood flow on 32 normal men between the ages of 38 and 79. It is planned to continue these studies so that a pattern of change for the individual decades can be determined, and so that additional correlative observations can be made on the subjects studied. PRESENT INVESTIGATIONMethods.-The subjects chosen for this study had been admitted to the hospital for minor elective operative procedures. All had been living normal lives consistent with their respective age group prior to admission, with no history to suggest any consequential pathology. An effort was made, by careful history taking and physical examination, to rule out significant clinical vascular disease, although some of the older subjects had such evidences of peripheral sclerosis as moderate thickening (to palpation) of the peripheral vessels, widening of the light reflex of the retinal arterioles, and occasional mild retinal arteriovenous nicking. In all instances the mental status was adjudged to be normal on the basis of a test pattern generally approved for gross psychological testing. Only those subjects whose arterial oxygen saturation was 94% or greater were considered acceptable ; those whose oxygen saturation was below this value were considered to have respiratory disease, even though other evidence for it was lacking. The latter subjects will be discussed separately, in a subsequent publication.

An epidemic caused by group C sulfonamide-resistant Neisseria meningitidis occurred during an eight-month period in two lower socioeconomic communities in Dade County, Florida. Five of 85 close contacts of patients (5.9%) contracted meningococcal disease. Nasopharyngeal carriage and serologic evidence of meningococcal infection were significantly more frequent among close contacts than among controls in the neighborhood. The risk of meningococcal infection was found to be significantly greater for persons who shared five-person bedrooms than for those who slept in less crowded bedrooms. A trial was conducted with rifampin among close contacts of patients. Rifampin eradicated meningococcal carriage in 92% of the treated group, and rifampin-resistant strains did not emerge. The data indicate the need for chemoprophylaxis of all close contacts of persons with meningococcal disease without regard for the results of nasopharyngeal cultures. Casual acquaintances (such as schoolmates) were not found to need prophylactic therapy.Neisseria meningitidis possesses the ability to cause outbreaks of life-threatening illness in otherwise healthy individuals [1][2][3][4][5]. Because of the dramatic swiftness with which meningitis or meningococcemia due to N. meningitidis can develop, considerable effort has been expended in development of preventive measures. Recently, the problem of prophylaxis has been complicated by the increase in prevalence of sulfonamide-resistant strains of N. meningitidis [6][7][8]. Studies in which serologic techniques have been used for identifi-

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