Modern Veterinary Care

More than 45,000 veterinarians currently practice medicine in the United States, primarily in private hospitals and clinics. Of these, about 60 percent treat small animals such as cats and dogs exclusively; about 10 percent treat large animals such as cattle and other livestock; and some 5 percent specialize in horses. The remainder treats both large and small animals. About 9,000 veterinarians in the United States work in corporations or public institutions, such as pharmaceutical companies, colleges or universities, or in local, state, or federal government agencies such as the United States Army Veterinary Corps. Typical small-animal veterinarians are family advisors as well as animal health care providers. They may help clients select an appropriate species or breed of pet and then guide them in the proper nutrition, grooming, training, and general husbandry of their new pet. A large portion of this practice involves preventive care, such as vaccinating, screening, and treating animals for internal and external parasites, as well as performing operations that prevent pets from bearing unwanted offspring. Small-animal veterinarians also treat their patients’ illnesses and injuries, address the owners’ concerns, and provide references to specialists when necessary. Another important responsibility of veterinarians is to provide humane euthanasia (the act of ending a patient’s life).

Large-animal veterinarians work primarily with livestock. They perform vaccinations, parasite control, and neutering, but there are several important differences. Large-animal veterinarians often treat groups of animals rather than individuals. They insure that infectious diseases do not spread from farm to farm. Most patients of large-animal veterinarians are viewed from the stand point of their economic potential.

They may perform artificial insemination on a herd of cows, treat a horse with

colic (severe abdominal pain), or assist a sow in delivering its piglets. Large-animal medicine and surgery is often practiced in stables, barns, and open fields rather than in animal hospitals. Veterinarians must, therefore, carry medicine and instruments with them wherever they go to face almost any challenge.

History of zoology

Humans have always been interested in the animals around them. They have benefited from learning about animals that are a source of food and clothing and other species that are harmful.

Animals were first classified in the 4th century BС by the Greek philosopher Aristotle, whose system was based on the similarity of organisms in shape and structure rather than on their phylogenetic lineage. Aristotle classified birds and bats together because they both had wings and could fly. The formal study of many fields of zoology began in the 15th and 16th centuries AD. In the 1500s the Italian artist Leonardo da Vinci and the Greek physician Andreas Veselius demonstrated that the internal anatomy of humans and other vertebrates was similar. The dissection of animals during the next two centuries led to numerous discoveries in anatomy and physiology. In the 1600s the invention of the microscope and the first observation of a single-celled animal, by Dutch microbiologist, Anthony van Leeuwenhoek, evoked new interest and excitement to the field of zoology.

Zoological discoveries at the microscopic level continued. During this period Francis Bacon and other scientists worked out general concepts of scientific observation and experimentation that are still in use.

In the 1750s an important advance was made by Swedish naturalist Carolus Linnaeus in the fields of taxonomy and systematics. Using some of the ideas of classification developed by John Ray during the late 1600s, Linnaeus devised a scheme for classifying plants and animals on the basis of their presumed phylogenetic relationships. Using the binomial names for genera and species to indicate the similarities between species, his system is still used.

The most dramatic development in zoology and all of biology was the 1859 publication of “On the Origin of Species by Means of Natural Selection” by Charles Darwin. Darwin's presentation of the concept of natural selection and evolution provided a universal explanation for the variations, similarities, and differences observed among all organisms. His thesis became the foundation on which modern zoology is based.

Mammals

Despite their size differences, the great blue whale and the pygmy shrew have something in common: they are both members of a warm-blooded, air-breathing class of vertebrate (backboned) animals known as Mammalia, or mammals. In many ways mammals are the most highly developed of all creatures.

The term mammal explains one important way in which creatures in this class are set apart from other animals. It comes from the Latin mamma, which means “breast”. Every female mammal has special glands, mammae that secrete milk. The females of all but the most primitive mamalian species are viviparous. This means they bear their young alive. The уоung are then fed with milk until they have grown enough to get food for themselves.

Hair is a typical mammalian feature. In many whales, however, it exists only in the fetal stages of development. Another basic trait of mammals is their highly developed brains – the most complex known. Particularly well developed is their cerebrum, the part of the brain that controls memory and learning. The mammalian brain enables the young to learn from the experience of their elders. Since the young mammal is dependent on its mother for nourishment, a period of learning is possible. This in turn has brought about a degree of behavioral adaptability unknown in any other group of organisms. Whales, seals, and dogs are among the most intelligent mammals, but monkeys, apes, and humans are the most intelligent of all.