Studies of the adsorption of human salivary proteins, in general, and the enzymes amylase, lysozyme, and neuraminidase, in particular, reveal that these proteins differ in their affinities for the surface of enamel. The enzymes studied retained their enzyme activity in the adsorbed state. Only amylase was desorbed by water; lysozyme was desorbed by its substrate; and all three enzymes, as well as most other adsorbed proteins, were desorbed by phosphate.Proteins are generally adsorbed at any interface: liquid/ gas, liquid/liquid, liquid/ solid. There are two significant consequences of this adsorption: (1) alterations occur in the secondary and tertiary structure of the adsorbed protein (usually in the direction of a less folded molecule), and (2) the properties, both physical and chemical, of the surface to which the protein is adsorbed are changed.From the point of view of the oral biologist, the questions raised by these phenomena are: (1) Which salivary proteins are adsorbed at the solid/liquid interface between tooth and saliva? (2) What are the specific effects of this adsorption on the properties of the tooth surface? and (3) Is it possible to alter the properties of the tooth surface, in vivo, by alterations in the adsorption process?The studies reported here are concerned with the first two questions. The adsorption to and elution of salivary proteins from human tooth enamel were studied under various conditions, and the effect of adsorption on the biological activity of various salivary enzymes was examined. 818Materials and Methods Carious material was removed from extracted human teeth, and the outer surface of the enamel was ground away to remove any adsorbed proteins. Enamel powder was then prepared from these teeth according to the method of Manly and Hodge.' The powder used was that which passed through a standard 100-mesh, but not a 200-mesh, sieve.Whole saliva was collected after the donor had rinsed his mouth thoroughly with water and was stimulated by chewing Parafilm. The first 10 ml were discarded, and the saliva samples were centrifuged for ten minutes at 20,000Xg at 5 C. Parotid secretion was collected by a modified Lashley CUp,2 and submandibular secretion by a Schneyer segregator. When parotid and submandibular salivas were collected simultaneously, half the submandibular saliva from the two submandibular glands was mixed with all the parotid saliva collected from one parotid gland during the same time period. A column of enamel powder was prepared using a 2.5-ml plastic syringe and 4 gm of 100-200-mesh enamel powder supported on a Whatman no. 1 paper disk. All solutions were pumped through the column at a constant flow rate. After flushing the column with water, 1 ml of saliva was run into the column and allowed to equilibrate for 45 minutes. The column proteins were subsequently eluted with various solutions, and the eluate was monitored using a microaperture flow cell in a Beckman DB-G spectrophotometer* at 280 mut. The column was eluted with water until the observed absorbance peak du...

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• Hydrogen clearance using the tissue polarographical electrode appears to be a potentially useful technique for intermittent measurements of rCBF in relatively small areas. Both chronic and acutely implanted electrodes were placed at different depths in rabbit cerebrum including cortex and subcortical gray and white matter. Polarographical electrodes, oppositely charged, sensing oxygen availability (O 2 a) also were implanted proximately for comparison of both rCBF response and O 2 a under conditions of normocapnia and hypercapnia. No functional difference was discerned between chronic and acute electrodes. Generally rates of blood flow were faster in gray matter than in white. Both monoexponential and biexponential curves, representing one and two compartments of blood flow, respectively, were observed in both gray and white matter. Some three-compartment curves also were seen. Hypercapnia generally induced faster rCBF in all compartments as well as increased O 2 a. Occasionally a change in compartmentalization was recorded from a single electrode during hypercapnia, and two instances of paradoxical decrease in rCBF were observed. A multicompartmental model with an arteriovenous thoroughfare shunt was postulated to account for the wide range of blood flow values recorded: from 5.2+ to 0.2 ml per gram per minute.Additional Key Words arteriovenous thoroughfare polarographical electrode hypercapnia