434 BACTERIA IN INFECTIOUS DISEASES. 



filled with the grains of rouge powder used by the 

 manufacturers for polishing these slides. These 

 little crypts, partly filled with grains of red or 

 yellow rouge powder, are very abundant on the 

 surface of some glass slides. 



And this recalls a mistake made by the writer 

 soon after his arrival in Havana in 1879. Upon 

 aspirating the air in front of my laboratory through 

 a small aperture, against a thin glass cover smeared 

 with glycerine, and examining this with a high 

 power (Zeiss -^ in.), it was found that a variety 

 of particles of considerable size, such as pollen 

 grains, spores of PemcttKum, starch grains, etc., had 

 been arrested ; and also that the specimen con- 

 tained a large number of spherical and rod-shaped 

 bodies, which were supposed to be bacteria. A 

 few days later, upon examining specimens of yel- 

 low fever blood spread upon thin glass covers, 

 similar bodies were discovered. Photo-micrographs 

 were made, which showed these minute spherical 

 and rod-like bodies interspersed among the blood- 

 corpuscles ; and distinguished physicians, who have 

 since inspected these photographs, have supposed, 

 before hearing an explanation of their real nature, 

 that they were really bacterial organisms. This 

 was my own opinion when I first saw them, but I 

 noticed that they did not seem to be in exactly 

 the same focal plane as the blood-corpuscles. I 

 therefore resorted to the simple expedient of wash- 

 ing the blood from the cover-glass and remounting 

 this over a circle of cement. Upon now examin- 



