534 



SCIENCE 



[N. S. Vol. XLII. No. 1085 



well from nearly all the higher forms of ani- 

 mal life, though the hemoglobin from the 

 pigeon as a rule gives a somewhat more abun- 

 dant growth. It is doubtful whether the 

 hemoglobin is necessary on account of its 

 nutritive properties, because extremely minute 

 quantities in media suffice for growth. The 

 phenomenon may be, therefore, a catalytic 

 one; but further study along this line is 

 needed to prove this point. 



There are other points concerning these bac- 

 teria which need further investigation, for 

 example, the phenomenon of symbiosis above 

 referred to. In this regard many bacteria oc- 

 curring in the lower animals should be studied 

 and we should also study and record more 

 thoroughly than has been done, the properties 

 of the non-pathogenic bacteria in this respect. 



This group of organisms it seems to me 

 has not received as much attention as it de- 

 serves by bacteriologists in general. To illus- 

 strate this, I might call attention to the fact 

 that in the very excellent and serviceable de- 

 scriptive chart for bacteria prepared by the 

 Committee on Methods of Identification of 

 Bacterial Species and endorsed by the Society 

 of American Bacteriologists no provision has 

 been made for recording the properties which 

 bacteria manifest toward blood. This not 

 only applies to the group of hemophilic bac- 

 teria but also to many bacteria which have 

 the property of hemolyzing blood and there- 

 fore commonly called hemolytic bacteria. 

 Hemolysis is an important characteristic of 

 certain bacteria, for example, streptococci, 

 cholera vibrios, etc., and being fairly constant 

 and quite readily determined by several 

 methods it has come to be of real practical 

 value in the identification and differentiation 

 of organisms. David John Davis 



TJNIVEKSITY OF ILLINOIS 



SPECIAL ARTICLES 

 ARTIFICIAL DAYLIGHT FOR THE MICROSCOPE 



An examination of the laboratories for stu- 

 dents, investigators and private workers with 

 the microscope in our country will show that 

 a very large number can not employ daylight, 

 but must depend on artificial light, although 



increasingly in biology and pathology stains of 

 all shades and combinations are used to color 

 the objects studied to bring out their structural 

 details. 



As daylight is the form of light for which 

 the human eye was developed in the course of 

 its evolution, and as it is the only light which 

 gives to the eye the true color values of the 

 objects in nature, and the multitudes of arti- 

 ficially colored objects in the industries, arts 

 and sciences, naturally many efforts have been 

 made to render artificial light more like day- 

 light. 



The accompanying diagram shows very stxi- 

 kingly the difference between daylight and the 

 light from a nitrogen-filled tungsten lamp. 

 The lamp-light is relatively too strong in all 

 the colors beyond the violet, and the difference 

 becomes very great in the green and the red. 

 In the other artificial lights commonly used, 

 except the arc, the difference from sunlight is 

 even greater. 



As can be readily seen, in order to render 

 any artificial light like daylight, the values of 

 the various colors of the spectrum must be like 

 those of daylight; and this can be attained 

 only by reducing the excess of the red, green 

 and other colors in the spectrum of the arti- 

 ficial light in such proportion as to make the 

 energy curve of its spectrum like that of the 

 sun. 



Until very recently all the efforts to make a 

 light filter or screen for artificial light which 

 would transmit light having daylight qualities 

 by which colors could be detected and dis- 

 criminated with the same certainty as in day- 

 light, were unsuccessful. 



During the last two years Dr. Henry Phelps 

 Gage, working in the laboratories of the Corn- 

 ing Glass-works, with the facilities there 

 found, has developed a glass filter which 

 renders the light from a nitrogen-filled tung- 

 sten lamp almost exactly like daylight. 

 In his own words : 



The investigation was started with the idea that 

 a very close approximation to the theoretical re- 

 quirements would be necessary, and the results 

 have justified the belief that the most perfect ap- 

 proximations are the best. 



