36 THE AMERICAN MONTHLY [Feb 
ome more notable each year. Especially is this the case 
with regard to practical problems in connection with the 
metallography of steel and of metal alloys. Workers 
like Sir W. C. Roberts-Austen, Mr. J. E. Stead, and others, 
have elevated the microscopic examination of such crystal- 
line structures into almost a distinct branch of science, 
The science of Bacteriology, however, is one that is of 
necessity universally accepted as coming peculiarly with- 
in the domain of microscopy, and it is in this department 
that many of the most interesting developments have 
taken place during the past year. Most noticeable of all 
was probably Professor Koch’s startling statement at the 
recent British Congress on Tuberculosis, which called 
forth swift and vehement protest. Professor Koch, 
whilst incidentally giving his adhesion to the theory that 
tuberculosis is, in contradiction to popular opinion, prac- 
tically non-hereditary, expressed the opinion that bovine 
tuberculosis was in reality not communicable to man, be- 
cause he had entirely failed in communicating human 
tuberculosis to cattle. The converse is manifest, but 
though Professor Koch observed that it was impossible 
to give this question a direct answer because the experi- 
mental investigation of it with human beings was out of 
the question, offers were almost immediately made by 
various persons to submit themselves to the test. We do 
not envy Dr. Koch his dilemma. 
Equally important has been the progress of the investi- 
gations into the causes and prevention of malaria, yel- 
low fever, elephantiasis, plague, distemper, and the aboli- 
tion of epidemics generally. The work of Major Ronald 
Ross and others not less devoted to the study has com- 
pletely disposed of the old theory that malaria was due 
to miasmatic vapors, and it is now proved, by the use 
of the microscope, beyond a doubt, that it is due to min- 
ute amcebula in the human blood, which pass part of their 
lives in certain species of mosquitoes, and by means of 
