WRIGHT'S METHOD OF COUNTING BACTERIA 135 



to lose any of the corpuscles in the successive washings. After 

 the last washing the corpuscles are sucked up into the pipette, 

 and the n saline up to the mark which indicated the volume of 

 the original blood. Such a mixture is taken, and, to prevent 

 loss of corpuscles, the pipette and tubes are washed with a 

 definite number of equal volumes of broth or saline. Thus 

 there can be obtained in a watch-glass a mixture of, say, one 

 volume of corpuscles and saline, and two volumes of the diluting 

 fluid. To this mixture is now added an appropriate number of 

 volumes, again measured in the same pipette, of the bacterial 

 emulsion to be counted, the amount, of course, depending upon 

 a rough judgment which with experience can be made of the 

 probable numbers present. A drop of the mixture is put under 

 a cover-glass, and the numbers of corpuscles on the one hand and 

 of bacteria on the other present in a number of fields are 

 counted. It is not necessary to stain the bacteria, but in the 

 case of motile organisms it is recommended that they be 

 rendered motionless by using as a diluent saline to which formol 

 has been added in the proportion of two or three drops to 10 c.c. 

 If the number of red blood corpuscles in the observer's blood be 

 known, it is evident that the amount of blood corresponding to 

 a certain number of blood corpuscles in a microscopic field can 

 be calculated, and the number of bacteria present in the same 

 amount of the mixture will be the number corresponding to the 

 number of corpuscles. Thus it is now only necessary to allow 

 for the dilution to obtain the number of bacteria in the original 

 emulsion. 



GENERAL BACTERIOLOGICAL DIAGNOSIS. 



Under this heading we have to consider the general routine 

 which is to be observed by the bacteriologist when any material 

 is submitted to him for examination. The object of such 

 examination may be to determine whether any organisms are 

 present, and if so, what organisms ; or the bacteriologist may 

 simply be asked whether a particular organism is or is not 

 present. In any case, his inquiry must consist (1) of a micro- 

 scopic examination of the material submitted ; (2) of an attempt 

 to isolate the organisms present ; and (3) of the identification of 

 the organisms isolated. We must, however, before considering 

 these points, look at a matter often neglected by those who seek 

 a bacteriological opinion, namely, the proper methods of ob- 

 toiniii'i and transferring to t/ie bacteriologist the material u'hich 

 I i' /.s to be asked to examine. The general principles here are 



