54 THE AMERICAN MONTHLY [Feb 
amining cultures, is that he finds a germ corresponding to 
the Klebs-Leeffler bacillus. It is for the physician to com- 
plete the diagnosis by putting with it the clinical symp- 
toms and to decide whether or not the disease process is 
in motion. 
There is such a wide range in the morphology of the 
diphtheria bacillus that it is not easy toidentify. There 
are other germs which resemble it so closely that it is 
sometimes difficult to distinguish them. The Leefiler ba- 
cillus may have all grades of virulence. The long varie- 
ty is the most virulent, yet the short form may be toxic 
and the non-virulent form cause death by strangulation. 
The site of the invasion may not be where the germs can 
be obtained, or antiseptic gargles may have been used. 
The culture medium may be contaminated. To proper- 
ly appreciate the value of microscopical evidence, a phy- 
sician should be familiar with those conditions which pro- 
mote accuracy and success. While it would be little short 
of criminal to discard the use of the microscope in the 
diagnosis of diphtheria, it should be kept in mind that 
there are conditions where this evidence may be absent 
and the patients life be dependent upon the recognition 
of the clinical symptoms. The diagnosis of scarlet fever 
is always important and sometimes difficuit. 
The rash may be slight and the clinical symptoms vids 
clear. If the physician has made a thorough study of 
the class coccus in relation to this disease, he will find it 
of value in making a diagnosis and in protecting suscep- 
tible individuals. In this case it is environment which 
causes malignancy. Scarlet fever is produced only by the 
multiplication of the infection in the blood of a suscepti- 
ble individual. 
This environment cannot be produced in the laboratory. 
If bacteriologists will take their microscopes to tbe scar- 
jet fever patient and study the germ under the conditions 
in which it causes disease, they will find evidence that it 
