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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Dental caries is the most common disease affecting mankind today. Its economic toll in the United States alone amounts to several billion dollars. To this must be added its toll in pain, loss of working time, and psychological distress.Despite the prevalence of this affliction and the amount of investigation it has engendered, its etiology remains obscure. In the past, many different microbial organisms have been indicted as the causative factor of the pathologic state. Among these, lactobacilli and streptococci enjoy favored positions.'-'In 1955, Orland, Blayney, Harrison, Reyniers, Trexler, Ervin, Gordon, and Wagner6 produced experimental dental caries by monoinoculating germfree rats with a particular strain of streptococcus. Subsequently, Fitzgerald, Jordan, and Stanley7 confirmed these findings in germfree rats, and Fitzgerald and Keyes8 have established the etiologic role of streptococci in hamster caries. Of a variety of organisms tested, only the specific streptococci were cariogenic. Their findings also disclosed a host specificity in the organisms, i.e., the rat strains produced caries only in the rat and not in the hamster, and the hamster strains produced caries only in the hamster and not in the rat. This specificity for the host and not for the tissue prompted the present investigation of the characteristics and methods of identification of these organisms. These studies of animal strains may provide clues for investigation of the bacterial etiology of human caries.Materials and Methods STREPTOCOCCAL GROUPING.-Streptococci have been separated into groups based on the presence of an immunologically distinct carbohydrate in the cell wall of the organisms.9-12 Cariogenic and non-cariogenic streptococci (hamster and rat strains) were provided by Dr. Robert Fitzgerald of the National Institute of Dental Research. As a preliminary step in the identification of cariogenic organisms, their reactivity with appropriate streptococcal antisera was tested to determine whether they belonged to any of the known groups of streptococci. The organisms were grown in 40-ml. quantities of Todd-Hewitt broth, and acid extracts were prepared by the method of Lancefield.9 These extracts have been used in microprecipitin tests'3 with group-specific streptococcal antisera, Groups A through S * PREPARATION OF ANTISERA.-As a further step in establishing the identity of cariogenic streptococci and to determine whether they belonged to a homogeneous group, antisera were prepared using rat (FA) and hamster (HS) strains as vaccines. Each of the two strains of cariogenic streptococci was grown in one liter of ToddHewitt broth supplemented with 0.5 per cent lactalbumin hydrolysate. The cultures were heat-killed at 560 C. for one hour and then divided into three parts for the preparation of three different types of vaccine: 1. A vaccine was prepared from whole organisms suspended in physiological saline

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