An overview of the basic principles of photochemistry is presented to facilitate discussion of fluorescence, quenching and quantum yields. These topics in turn provide the foundation for an account of fluorescence spectroscopy and its application to microscopy. A brief overview of light microscopy and the application of fluorescence microscopy is given. The influences of molecular features, such as aromatic character and substitution patterns, on color and fluorescence are described. The concept of color fading is considered with particular reference to its effect on microscopic preparations. A survey of representative fluorescent probes is provided, and their sensitivity, application, and limitations are described. The phototoxicity of fluorescent molecules is discussed using biomembranes and DNA as examples of targets of toxicity. Photodynamic therapy, a relatively new clinical application of phototoxicity, is described. Both anticancer and antimicrobial applications are noted, and an assessment is given of the current ideas on the ideal physicochemical properties of the sensitizing agents for such applications.

Definite to strong carcinogenic activity has been shown by some monosubstituted and disubstituted derivatives of .1"3 The only active trisubstituted-DAB tested has been the 2',4',6'-trifluoro derivative.4 It seemed of interest to synthesize and test for rat hepatocarcinogenic activity all of the trimethyl homologs of DAB with Me groups in the primed positions only. These are all new compounds and can be prepared by the diazotization of the proper trimethylanilines followed by coupling with PhNMe2. The new azo compounds are listed in Table 1. Experimental SectionAll melting points were detd on a Fisher-Johns apparatus and are uncorrected. The C, , N analyses were performed in this department on an F and M Model 185 analyzer by Mr. Daryl Sharp.Where analyses are indicated only by symbols of the elements analytical results obtained for those elements were within ±0.4% of the theoretical values.Trimethylanilines. Mesidine,5 bp 224-228°, was prepd from nitromesitylene6 by reduction with Sn-HCl. 5-Aminopseudocumene,1 mp 62-63°, was prepd from 5-nitropseudocumene8 in the same way. 4-Aminohemimellitene,8 mp 29-27°, was obtd from 5-nitrohemimellitene,8 6-aminopseudocumene9 was prepd from 6-nitropseudocumene,10 and 5-aminohemimellitene,11 mp 75-78°, was prepared from 5-nitrohemimellitene8 by reduction (Fe-AcOH). 3-Amino-pseudocumene9 was produced by Fe-AcOH reduction of 3-nitropseudocumene which in turn was produced by the hypophosphorus acid reduction of the diazonium salt from 3-nitro-6-aminopseudocumene.12 2',4',6'-Trimethyl-DAB. Mesidine (60 g) was dissolved in a mixt of 113 ml of coned HC1 and 376 ml of H,0 and diazotized at 0°u sing 30.6 g of NaN02 in 150 ml of , . One-half hr after the final addn, a soln of 54 g of C6H5NMe2, 552 ml of 95% EtOH, 264 ml of HjO, and 109 g of NaOAc was added, and the soln was stirred for 24 hr. Extn with PhH and evapn of PhH left a semisolid material which

A Y-piece is inserted s o r l5cm before the respirator control, one limb of which is occluded by a normal 0 . 5~1 gas tap. This enables the respirator to be turned on and off without switching the con pressor, which is normally located outside the theatre to lessen noise. A Vitalograp condenser humidifier is placed between the patient and the respirator. Tested against a 'dummy lung' with a n 8mm endotracheal tube and a compliance c 50ml/cm H 2O gauge the output of the EMO is 0.5 % higher than indicated at the 3 mark with a minute volume of 6 litresimin reducing to plus 0.4% at 10 litres/min.