Most of the veterinarians 50 years ago were practitioners only. There was little or no specialization. They were seldom asked to look at a hog, chicken or a dog. Indeed, some felt it was beneath their professional dignity to do so. Discoveries in the medical and veterinary sciences as well as a changing economic world made possible more accurate diagnoses and therapeutics. The veterinarian was forced to recognize that other animals besides the horse were worthy of his attention. The whole field was thus expanded to such an extent that today no individual can hope to become proficient in all phases of the science or even to be well versed in all phases. It is necessary to choose that branch of the profession which best suits him and pursue it.