456 



Mr. G. F. DowdeswelL 



[Jan. 18, 



difficult to examine ; it is a form of Bacterium, but when stained is 

 readily recognised by the size of the cells, which is but little variable, 

 and by its form, which is distinctive.* The numbers in which it appears 

 in the blood in different cases, in various portions of the same blood, 

 or even in different parts of the same preparation, are very variable ; 

 this appears to arise in some measure from a disposition to agglome- 

 rate together in places, and may be due to the tendency of the blood 

 to coagulate. To enumerate these organisms in unstained prepara- 

 tions is impossible with any of our present microscopical appliances, 

 as they cannot be sufficiently clearly distinguished, and in dried and 

 stained preparations, not knowing the depth of the layer of blood, 

 it can only be done by comparison with the number of the red cor- 

 puscles, obviously a rough and uncertain method. In some cases, 

 however, they are fully ten times as numerous as the red corpuscles, 

 and taking the number of the latter at about 5,000,000 to the cubic 

 millimetre, we have of the former, 50,000,000, or in a drop upwards 

 of 3,000,000,000, which corresponds as nearly as could be expected 

 from their variable numbers and irregular distribution to the 

 minimal quantities in which I have found the blood to be infec- 

 tive, viz., almost invariably in the 100 millionth of a drop ;t in 

 much smaller quantities its action is uncertain, in correspondence 

 with the view that the microphyte does constitute the active con- 

 tagium ; for in that case, or if the contagium be particulate, what- 

 ever its intimate nature, to whatever degree the fluid in which 

 it is contained may be divided by successive dilution, it is evident 

 that any given portion may, and some one or more portions must, 

 contain the infective particle; and hence that to determine the 

 least quantity in which it is constantly infective is impracticable. 

 From the dimensions of the organisms and the numbers that can be 

 comprised in a given space, J it is evident that blood containing 

 them cannot be constantly infective in the quantities stated by some 

 observers, viz., in the trillionth of a drop or less, yet it might be so 

 exceptionally, and consequently the original statement of Davaine 

 may have been strictly correct, in the instances he has recorded, 

 though the inference usually drawn from them is erroneous. 



In regard to the origination of infection by putrid blood, in several 

 series of experiments, I have found that during the summer and 



* Its characters I bare already described (" Journ. E. Micros. Soc," 1882, vol. ii, 

 p. 310) : it is easily distinguished from B. termo, which, it superficially resembles, by 

 its size ; being but half the breadth fO'o p), and by its form ; the cell-wall not being 

 constricted in the centre as in the latter species. 



f In one instance I found 10 gtt. of the blood diluted 10,000,000,000 times fatally 

 infective within about the usual period. 



% "Viz., as already shown ("Journ. Eoy. Micros. Soc," 1882, p. 311), 

 250,000,000,000 in a drop taken as the sixteenth part of a cub. centim. 



