YELLOW FEVER. 425 



photo-micrographs taken. From the manner in which 

 these granules refract light, and for other reasons, they 

 are believed by Dr. Steinberg to be fat, and to represent 

 a fatty degeneration of the leucocytes. 



" The blood of twelve healthy individuals was exam- 

 ined in Havana for comparison, and in nearly every case 

 an occasional leucocyte was found to contain a few (one 

 or two) granules undistinguishable from those found in 

 the blood of yellow fever ; but this was the rare excep- 

 tion ; while in severe cases of yellow fever the granules 

 were abundant, and nearly every white corpuscle con- 

 tained -some of them." 



The granules referred to are well seen in the 

 heliotype reproductions of the writer's photo- 

 micrographs made in Havana. (See Figs. 1, 2, 

 3, and 4, Plate XII.) 



Upon comparing the granules referred to, as 

 seen in Fig. 3, Plate XII., with a photo-micrograph 

 of the spores of bacilli (Fig. 3, Plate VIII.) made 

 with the same amplification, a very striking resem- 

 blance will be noticed. Indeed it would be impos- 

 sible to determine from the optical appearances 

 alone that in one case we are dealing with fat- 

 granules, and in the other with reproductive spores. 

 The size and the refractive index are the same, or 

 very nearly so. These granules were new to the 

 writer when he first encountered them in the 

 blood of yellow fever patients, and it seemed not 

 improbable that a discovery of value had been 

 made. Much time was accordingly given to their 

 study. The result of this was to convince the writer 

 that they were fat-granules, probably developed in 



