72 G. F. DOWDESWELL. 



within the white corpuscles, which are considerably swollen and 

 altered. It also is a true Bacillus, sometimes, though not very 

 frequently, forming moderately long filaments of several articu- 

 lations, which, from their mode of union, must possess flagella ; 

 though these would be of inestimable tenuity, the Bacilli them- 

 selves verging on the confines of the invisible with the very best 

 optical appliances and arrangements, and being, I believe, the 

 most minute independent organisms yet described. In the 

 lungs this Bacillus is also found, sometimes in vast numbers, 

 but confined to the blood-vessels, both the larger vessels and the 

 capillaries. Here in a successful preparation the deeply-stained 

 white corpuscles filled with these organisms are readily seen. 

 The Bacilli are also found lying thickly on the inner walls of the 

 vessels ; but to resolve the individual forms distinctly requires a 

 magnifying power of 12,000 or 14,000 diameters at least, and 

 good illumination. The general appearance which they present 

 is shown in the accompanying plate (fig. 1), which is an accu- 

 rate representation of a section of lung which has been 

 treated with a strong solution of sodic carbonate after the 

 steps above described. Tliis has rendered the tissues pale and 

 somewhat indistinct, while the deeply-stained masses of Bacilli 

 within the white corpuscles are conspicuous in the different 

 blood-vessels; but the amplification in the drawing is not 

 nearly sufficient to show the individual forms on the walls of the 

 vessels. 



The relative size and form of these Bacilli is given in fig. 3, as 

 shown under a magnifying power of nearly 3000 diams. This 

 is the organism described and figured by Dr. Koch as B. septi- 

 cemia, and regarded by him as the specific infection, the true 

 coutagium of the disease ; and as he very kindly gave me some 

 of his own preparations during his recent visit here, I have been 

 enabled directly to compare the organisms which occur in both 

 his and my own, and find them identical. i 



Por staining these preparations a solution of methyl aniline 



tions in the standard employed must be borne in mind. 1 have found 

 considerable difference between the scales of different makers wliich I have. 

 Hitherto there has been no standard micrometer scale for reference ; one, 

 liowever, has now been completed by Professor liogers of Cambridge, 

 U.S.A., of which microscopists will no doubt largely avail themselves. 



^ These minute organisms form an excellent test for any high power 

 objective, but I may here mention that the best possible independent object, 

 as distinguished from a mere line or marking, is a minute barb on the point 

 of the head of the spermatozoon of the newt {Triton cris/atus), well known 

 as possessing a large and conspicuous " filament." This barb was first 

 observed and shown to me by Mr. Nelson, the accomplished diatomist of 

 Marlborough Hill, St. John's Wood, to whom I am also indebted for assist- 

 ance in the measurement and examination of these most minute micro- 

 scopical objects. 



