128 
TENTH REPORT. 
and preserved in sealed glass tubes. It is well to add 0.2 per cent of lysol 
or some other preservative to guard against contamination when opened. 
In counting it is convenient to have the field of the microscope divided by 
cross hairs, as shown in Fig. 26. This can be readily accomplished b} r placing 
• hairs on the diaphragm of the eyepiece, as shown in Fig. 27. Select a good, 
straight, black hair, cut off four pieces of suitable length. Spread a little 
cedar oil on the diaphragm, and by means of tweezers place the hairs in 
position, spacing them so that the central square is about one-third of the 
diameter of the opening. Replace the eye-piece in the microscope, and if 
the hairs are not visible and sharp, the diaphragm must be moved until 
they are in focus. 
Dosage . — In administering bacterial vac- 
cines for therapeutic purposes, the fre- 
quency of administration and the size of 
the doses depend on the kind of vaccine 
used and on the patient. As a general rule, 
that dose should be given which gives the 
maximum of positive phase consistent with 
the minimum of negative phase (see Fig. 
28). In round numbers, the doses fre- 
quently used for the various bacteria are 
as follows: Staphylococcus 300.000,000, 
pneumococcus and streptococcus 50,000,000, gonococcus 10,000,000, tuber- 
cle (T. R.) 1-3000 mg. to 1-800 mg. It is always best to begin with a 
small dose and work up, as some patients can stand two or three times as 
much as others. 
Fig. 27.— Diaphragm of eyepiece 
showing hairs in position. 
Fig. 28. — Opsonic curve showing constituent parts (after 
Ross.) 
The Pool . — The opsonic index of a serum expresses the ratio which its 
phagocytic index bears to the phagocytic index of “ normal serum. ” Nor- 
mal serum in this sense would be serum that had never been influenced by 
the particular bacterium in question. Owing, however, to the limitations 
of our knowledge, this is quite an impractical standard, and hence resort is 
had to pooling the blood serum of several presumably normal persons. Each 
person is bled in the usual way, and after the serum separates equal portions 
of the sera are taken and mixed. This mixed serum is the pool. If great 
accuracy is desired, each constituent serum should be tested against the 
