540 



HANDBOOK OF PHYSIOLOGY 



NEUROPHYSIOLOGY I 



pecially pressure, determine the threshold in the 

 blast injection technique and that the threshold so 

 determined is not related to odor concentration. 



Since neither subjective sniffing nor the substitu- 

 tion of an air blast for the observer's own sniff dispose 

 of many of the difficulties in odor threshold measure- 

 ment, Wenzel (88) has studied the reliability of 

 threshold measurements during normal breathing 

 with the subject's head placed in a camera inodorata. 

 Here a plastic box encloses the subject's head, and 

 the hair and face can be covered with plastic to 

 eliminate their odors, leaving only the nostrils ex- 

 posed. A continuous stream of pure air to which 

 odors can be added is fed into the box. This method 

 is claimed to give satisfactory results in threshold 

 measurement without the need for prior training of 

 the subject. 



It has been claimed that subjects can match odors 

 quantitatively by the use of a standard "sniff' tech- 

 nique, using as test substances two aliphatic homol- 

 ogous series, comprised of the alcohols butanol (CO 

 through duodecanol (Cii), and the acetate esters 

 hexyl (Ce) through duodecyl (C12), each prepared in 

 serial dilutions (19). No attempt was made in these 

 tests to instruct the subject in the technique of sniffing, 

 reliance being placed on the subject's existing habits. 

 Results were consistent in repeated trials, with odor- 

 osity decreasing as a function of molecular chain 

 length, and also with dilution, for both alcohols and 

 acetates. 



Kuehner (61) has used an air-dilution method in 

 determining olfactory thresholds and stresses the 

 need to standardize the subject from day to day by 

 exposing him to standard vapor concentrations. Ex- 

 treme variations of sensitivity noted in individuals 

 make it impossible to take odor measurements over 

 extended periods without knowledge of the subject's 

 sensitivity at the time of sampling. One breath of 

 ammonia can reduce the sensitivity by 50 per cent 

 for 24 hr. At the onset of a head cold, the sensitivity 

 is sharply increased but later is depressed. A marked 

 temporary reduction in sensitivity follows excessive 

 drinking or smoking. Kuehner used air saturated 

 with xylene vapor as a reference odor and in a pro- 

 longed series of experiments with two subjects ex- 

 hibiting similar sensitivities found that its normal 

 odor level was 380 times greater than threshold. 

 Under the same conditions, nicotine saturated air to 

 3000 times the threshold intensity. 



OBJECTIVE ME.\SUREMENT TECHNIQUES. Kuchner (6l) 



claims that odorous substances are capable of react- 



ina; with oxidants and that the resulting deodoriza- 

 tion is related to the amount of oxidant reduced. 

 While efforts to find reproducible concentrations of 

 individual odors in a complex, such as tobacco smoke, 

 were unsuccessful, it was found that certain oxidants 

 react with odor complexes in a reproducible manner, 

 thus confirming the earlier observations of Lang et al. 

 (62). Kuehner found a close uniformity in odor pro- 

 duction by tobacco artificially burned in this system 

 regardless of type, freshness and rate of combustion, 

 and established that tobacco smoked by humans 

 produced only 40 per cent of the odor level of that 

 'smoked' artificially, both in its reducing powers with 

 oxidants and as determined subjectively under room 

 conditions. This technique has been criticized by 

 Turk (85) on the grounds that cxidant methods, 

 which usually employ permanganates or eerie salts, 

 may be inadequate because of a lack of relationship 

 between quality or intensity of odorants and their 

 reactivity toward a chemical oxidant. Such methods 

 may indicate only the reducing or oxidizing qualities 

 of the extraneous atmospheric gases and vapors. 



Turk (85) has used infrared adsorption spectra of 

 odorous substances as a means of qualitative analysis. 

 Different functional groups, such as aldehyde, alco- 

 hol and ester linkages, show typical infrared adsorp- 

 tion frequencies. Thus the infrared spectrum of a 

 mixture of compounds reveals information on the 

 types of individual compounds therein, and by this 

 means Turk has been able to detect vaporized mineral 

 oil as a component of apple aroma in commercial 

 apple storage rooms. It has already been mentioned 

 that this method may not be free from error, since 

 substances with similar odors may have different ad- 

 sorption spectra and vice versa (87, 89). 



ELECTRICAL PHENOMEN.A IN OLF.ACTORY BULB 

 .ACCOMP.ANYING OLF.ACTORY STIMUL.ATION 



Patterns of Spontanrous and Induced Activity in Bulb 

 and Effects of Anesthesia 



The rhvthmic waxes that can be recorded from 

 the surface of the bull) have been extensively investi- 

 gated (4-10, 72, 86). Whereas Adrian's initial ex- 

 periments suggested rhythmic discharges in the bulb 

 svnchronously with each ijieath, later experiments 

 (5, 9) have shown that with filtered air no mechanical 

 stimulation occurs. Both spontaneous waves and 

 those which occur in response to strong olfactory 

 stimuli have been recorded in the bulb. 



