BIOLOGICAL PRODUCTS (VETERINARY).* 
By Robert H. Wilson, D.V.M., Detroit, Mich. 
The rapid advances made in recent years in microbiology 
have given a clearer conception of disease and its processes. The 
extensive investigations of infection, immunity and their various 
phenomena have resulted in the development of new methods of 
diagnosis, prevention and treatment of specific infectious dis¬ 
eases, through products of biological origin. These products, 
which include toxins, antisera and vaccines, are of bacterial origin 
and consist of the substances resulting from bacterial growth of 
the reactive agents in the blood of animals treated with bacteria, 
or their toxins, and of bacteria modified more or less. 
It is only within the past few years that biological products 
have been employed extensively in veterinary medicine. There 
has existed more or less prejudice against them on account of 
their expense and apparent inefficiency in some cases. But this 
prejudice has been practically eliminated, and the demand for the 
products would indicate that their practical value in most in¬ 
stances has been proven without a doubt. The products which 
have been developed recently have met with general favor, for 
the modern veterinarian, like the human practitioner, is ever alert 
to acquire methods that will materially aid him in his chosen 
work. 
Before taking up a discussion of the various biological prod¬ 
ucts used in veterinary medicine, it will be well to review briefly 
the subject of immunity, for it is on this all important subject 
and its phenomena that the biological products have their .basis. 
By immunity is meant resistance, or non-susceptibility to a 
disease or an organism, or its metabolic products, either under 
* Read before the February, T912, meeting, Michigan State Veterinary Medical 
Association.- Research Laboratory, Parke, Davis & Co. 
668 
