20 PRINCIPLES OF ANIMAL BIOLOGY 



somes were observed (1880-1910) to behave in certain wa3\s before their 

 genetic significance was understood. Later the order of discovery was 

 reversed; the demonstrated workings of heredity required that the 

 chromosomes should operate in a certain manner, and in many cases their 

 behavior has been subsequently found to coincide with the theoretical 

 expectation. 



General Physiology. — While stains, smears, section-cutting apparatus, 

 and improved microscopes have been the traditional tools of the cytolo- 

 gists, recent work in that field has dealt with living cells and has included 

 minute dissection of cells by means of ingenious devices which can be 

 operated under the microscope. This phase of cytology borders closely 

 upon general physiology, which deals with fundamental activities of 

 protoplasm. General physiology is concerned with chemical composition 

 and reactions of living matter, permeability, viscosity, colloid structure, 

 electrical charges, transformations of energy, etc., in an attempt to relate 

 these conditions or processes to the phenomena of life. The material 

 used in such studies is partly a host of one-celled organisms, partly the 

 eggs of various aquatic forms, and partly the specialized masses of cells, 

 or tissues, of higher animals. Although these cells differ much in 

 appearance and in their ultimate fate, they must do certain fundamental 

 things in common. It is in the province of general physiology to discover 

 these common processes. This development is comparatively recent, 

 and a large number of biologists at the present time are engaged in this 

 type of work. 



Change in Content of Biology. — It will have been observed that 

 throughout the development of biology, from the early Greeks to the 

 present time, the bulk of what was known regarding living things con- 

 cerned their structure. This branch of biology is known as moryhology . 

 At first little else was known, and in the Middle Ages the continuity of 

 biology hung on the one thread of anatomy. Only gradually did the 

 functions of organs come to be of much interest, and William Harvey, in 

 the seventeenth century, is often regarded as the founder of -physiology. 

 At first a study of mechanics, physiology later became concerned with 

 the principles of organic chemistry. Attempts were made to apply 

 these principles not only to the workings of the organs of the adult but 

 to the processes of embryonic development. Embryology thus became 

 physiological as well as morphological, and modern work in embryology 

 is chiefly of the former kind. 



Simultaneously with physiology there grew up the science of classifica- 

 tion, or taxonomy. At first, as developed by Linnaeus, classification was 

 arbitrary. Though similar animals were grouped together, their similar- 

 ity was not held to have any significance. A century later, when evolu- 

 tion was generally accepted, the basis of taxonomy came to be kinship. 



