70 RELATIONSHIPS OF THE COCCACE/E 



of the hues on white paper. This color chart is re- 

 produced as the frontispiece of the book. The nine 

 hues, passing from left to right, we have designated as 

 White, Light Lemon Yellow, Light Cadmium Yellow, 

 Medium Cadmium Yellow, Orange Yellow, Cadmium 

 Orange, Orange Red, Medium Red, Dark Red. The 

 chroma is indicated by a number which corresponds 

 to the number of washes of the hue applied, ranging from 

 I to IX. 



We did not make a study of the pigments formed, 

 from the chemical standpoint, altho this subject holds 

 out promise of significant results. Schneider (1897) 

 made many observations upon the solubility of bacterial 

 pigments in various liquids, and upon the effect of 

 acids, alkalies, etc., upon the solutions obtained. 

 The results are cited in considerable detail by Migula 

 (1900) in his systematic account of the particular organ- 

 isms studied. The results are sufficiently suggestive to 

 make further work along this line eminently desirable. 



Liquefaction of gelatin. The liquefaction of gelatin, 

 like the property of pigment production, is subject to 

 considerable variations. Kruse (1896), for example, 

 found that staphylococci lose their liquefying power after 

 prolonged cultivation under anaerobic conditions. Spon- 

 taneous variations, too, may occur under approximately 

 uniform environmental conditions. Conn (1900) was 

 able by selection to obtain from a single culture of a 

 milk coccus two extreme variants, one a rapidly lique- 



