A SPECTROPHOTOMETRIC DEVELOPMENT FOR BIO- 

 LOGICAL AND PHOTOCHEMICAL INVESTIGATIONS 



By F. S. BRACKETT and E. D. McALISTER 

 Division of Radiation and Organisms. Smithsonian Institution 



(With Three Plates) 



Investigations of the effect of radiation upon biological material can 

 be carried out advantageously with microscopic organisms such as 

 unicellular algae, bacteria, yeast, and fungi, along lines closely 

 analogous to customary spectroscopic practice. The great advantage 

 of this general method of approach is that one is able to obtain 

 numerical evaluations which depend statistically on large numbers 

 of organisms without going to equipment of cumbersome dimensions. 

 The needs are, however, sufficiently different as to make desirable the 

 development of special equipment and methods. It is our purpose to 

 describe the development along these lines which has been undertaken 

 in the Division of Radiation and Organisms, with a view to carrying 

 out cooperative investigations with biologists who have specialized 

 in the study of particular types of small organisms. It has been our 

 idea to make the special equipment developed available not only to 

 members of the Division but more generally to biologists who may 

 arrange to carry on investigations at the Smithsonian Institution m 

 cooperation with the Division. 



The first of these cooperative experiments has been carried out with 

 Dr. Florence E. Meier, National Research Fellow, working with the 

 alga ChlorcUa vulgaris of her collection. The results of her experi- 

 ments have been presented in a previous publication. Smithsonian 

 Miscellaneous Collections, Vol. 87, No. 10, 1932. Some of the prob- 

 lems of a physical nature which have arisen in the course of these 

 experiments will be taken up in connection with this discussion. 



In order that advantage may be gained from comparative observa- 

 tions of a differential type it is desirable that the organisms be ex- 

 posed to several wave lengths at the same time. Where slides can be 

 prepared coated with a layer of microscopic organisms, they may be 

 exposed in an instrument of the spectrograph type. Since, however, 

 there exist essential difficulties in securing either as great uniformity 

 or as fine texture or structure as is presented by the photographic 

 plate, it is desirable to secure as large an area exposed to a given wave 



Smithsonian Miscellaneous Collections, Vol. 87, No. 12 



